Belatacept Combined With Transient Calcineurin Inhibitor Therapy Prevents Rejection and Promotes Improved Long-Term Renal Allograft Function.

Belatacept, a T cell costimulation blocker, demonstrated superior renal function, lower cardiovascular risk, and improved graft and patient survival in renal transplant recipients. Despite the potential benefits, adoption of belatacept has been limited in part due to concerns regarding higher rates and grades of acute rejection in clinical trials. Since July 2011, we have utilized belatacept-based immunosuppression regimens in clinical practice. In this retrospective analysis of 745 patients undergoing renal transplantation at our center, we compared patients treated with belatacept (n = 535) with a historical cohort receiving a tacrolimus-based protocol (n = 205). Patient and graft survival were equivalent for all groups. An increased rate of acute rejection was observed in an initial cohort treated with a protocol similar to the low-intensity regimen from the BENEFIT trial versus the historical tacrolimus group (50.5% vs. 20.5%). The addition of a transient course of tacrolimus reduced rejection rates to acceptable levels (16%). Treatment with belatacept was associated with superior estimated GFR (belatacept 63.8 mL/min vs. tacrolimus 46.2 mL/min at 4 years, p < 0.0001). There were no differences in serious infections including rates of cytomegalovirus or BK viremia. We describe the development of a costimulatory blockade-based strategy that ultimately allows renal transplant recipients to achieve calcineurin inhibitor-free immunosuppression.

Postdepletion Lymphocyte Reconstitution During Belatacept and Rapamycin Treatment in Kidney Transplant Recipients.

Belatacept is used to prevent allograft rejection but fails to do so in a sizable minority of patients due to inadequate control of costimulation-resistant T cells. In this study, we report control of costimulation-resistant rejection when belatacept was combined with perioperative alemtuzumab-mediated lymphocyte depletion and rapamycin. To assess the means by which the alemtuzumab, belatacept and rapamycin (ABR) regimen controls belatacept-resistant rejection, we studied 20 ABR-treated patients and characterized peripheral lymphocyte phenotype and functional responses to donor, third-party and viral antigens using flow cytometry, intracellular cytokine staining and carboxyfluorescein succinimidyl ester-based lymphocyte proliferation. Compared with conventional immunosuppression in 10 patients, lymphocyte depletion evoked substantial homeostatic lymphocyte activation balanced by regulatory T and B cell phenotypes. The reconstituted T cell repertoire was enriched for CD28(+) naïve cells, notably diminished in belatacept-resistant CD28(-) memory subsets and depleted of polyfunctional donor-specific T cells but able to respond to third-party and latent herpes viruses. B cell responses were similarly favorable, without alloantibody development and a reduction in memory subsets-changes not seen in conventionally treated patients. The ABR regimen uniquely altered the immune profile, producing a repertoire enriched for CD28(+) T cells, hyporesponsive to donor alloantigen and competent in its protective immune capabilities. The resulting repertoire was permissive for control of rejection with belatacept monotherapy.

Renal transplantation using belatacept without maintenance steroids or calcineurin inhibitors.

Kidney transplantation remains limited by toxicities of calcineurin inhibitors (CNIs) and steroids. Belatacept is a less toxic CNI alternative, but existing regimens rely on steroids and have higher rejection rates. Experimentally, donor bone marrow and sirolimus promote belatacept's efficacy. To investigate a belatacept-based regimen without CNIs or steroids, we transplanted recipients of live donor kidneys using alemtuzumab induction, monthly belatacept and daily sirolimus. Patients were randomized 1:1 to receive unfractionated donor bone marrow. After 1 year, patients were allowed to wean from sirolimus. Patients were followed clinically and with surveillance biopsies. Twenty patients were transplanted, all successfully. Mean creatinine (estimated GFR) was 1.10 ± 0.07 mg/dL (89 ± 3.56 mL/min) and 1.13 ± 0.07 mg/dL (and 88 ± 3.48 mL/min) at 12 and 36 months, respectively. Excellent results were achieved irrespective of bone marrow infusion. Ten patients elected oral immunosuppressant weaning, seven of whom were maintained rejection-free on monotherapy belatacept. Those failing to wean were successfully maintained on belatacept-based regimens supplemented by oral immunosuppression. Seven patients declined immunosuppressant weaning and three patients were denied weaning for associated medical conditions; all remained rejection-free. Belatacept and sirolimus effectively prevent kidney allograft rejection without CNIs or steroids when used following alemtuzumab induction. Selected, immunologically low-risk patients can be maintained solely on once monthly intravenous belatacept.

Elastic and inelastic diffraction changes upon variation of the relative humidity environment of PurE crystals.

The different changes observed in the diffraction patterns of three different crystal forms (hexagonal, trigonal and monoclinic) of PurE (EC 4.1.1.21), an enzyme from the purine-biosynthesis pathway of Bacillus anthracis, upon a wide range of changes in the relative humidity environment of the crystals are documented. In addition, the changes in the unit-cell parameters, volume and bulk solvent in the three different crystal forms were systematically followed. In an attempt to explain the elastic (P6(5)22) and inelastic (P3(1)21) changes in the diffraction pattern, refined structures of the three different crystal forms determined at 100 K are presented, with particular emphasis on the tertiary and quaternary structural differences, crystal packing, intermolecular and intramolecular interactions and solvent structure. The refined structures show that the precipitant salts, solvent structure (both ordered and bulk) and conformation of the C-termini all play a role in creating a unique cement at both the intramolecular and intermolecular contacts of the different crystal forms. It is suggested that it is the combination of polyethylene glycol and the structure of the ordered water molecules (first and second layers) as well as the structure of the bulk solvent that are the critical factors in the plasticity of the hexagonal crystal packing as opposed to the inelastic responses of the lower symmetry forms.

Humidity control can compensate for the damage induced in protein crystals by alien solutions.

The use of relative humidity control of protein crystals to overcome some of the shortcomings of soaking ligands (i.e. inhibitors, substrate analogs, weak ligands) into pre-grown apoprotein crystals has been explored. Crystals of PurE (EC 4.1.1.21), an enzyme from the purine-biosynthesis pathway of Bacillus anthracis, were used as a test case. The findings can be summarized as follows: (i) using humidity control, it is possible to improve/optimize the diffraction quality of crystals soaked in solutions of organic solvent (DMSO, ethanol) containing ligands/inhibitors; (ii) optimization of the relative humidity can compensate for the deterioration of the diffraction pattern that is observed upon desalting crystals grown in high salt; (iii) combining desalting protocols with the addition of PEG it is possible to achieve very high concentrations of weak ligands (in the 5-10 mM range) in soaking solutions and (iv) fine control of the relative humidity of crystals soaked in these solutions can compensate for the deterioration of crystal diffraction and restore `high-resolution' diffraction for structure-based and fragment-based drug design. It is suggested that these experimental protocols may be useful in other protein systems and may be applicable in academic or private research to increase the probability of obtaining structures of protein-ligand complexes at high resolution.

Clinical and economic burden of community-onset multidrug-resistant infections requiring hospitalization.

OBJECTIVES: To analyze the clinical and economic burden of community-acquired (CA) or community-onset healthcare-associated (COHCA) multidrug-resistant (MDR) infections requiring hospitalization. METHODS: Case-control study. Adults admitted with CA or COHCA MDR infections were considered cases, while those admitted in the same period with non-MDR infections were controls. The matching criteria were source of infection and/or microorganism. Primary outcome was 30-day clinical failure. Secondary outcomes were 90-day and 1-year mortality, hospitalization costs and resource consumption. RESULTS: 194 patients (97 cases and 97 controls) were included. Multivariate analysis identified age (odds ratio [OR], 1.07, 95% confidence interval [CI], 1.01-1.14) and SOFA score (OR, 1.45, CI95%, 1.15-1.84) as independent predictors of 30-day clinical failure. Age (hazard ratio [HR] 1.09, 95%CI, 1.03-1.16) was the only factor associated with 90-day mortality, whereas age (HR 1.06, 95%CI, 1.03-1.09) and Charlson Index (HR 1.2, 95%CI, 1.07-1.34) were associated with 1-year mortality. MDR group showed longer hospitalization (p<0.001) and MDR hospitalization costs almost doubled those in the non-MDR group. MDR infections were associated with higher antimicrobial costs. CONCLUSIONS: Worse economic outcomes were identified with community-onset MDR infections. MDR was associated with worse clinical outcomes but mainly due to higher comorbidity of patients in MDR group, rather than multidrug resistance.

Charge selectivity of the glomerular filtration barrier in healthy and nephrotic humans.

We used dextran sulfate (DS) to evaluate barrier charge selectivity in 11 nonproteinuric subjects and in 11 patients with the nephrotic syndrome due to either membranous nephropathy or minimal change nephropathy. The 3H-DS preparation spanned a molecular radius interval of 10-24 A and exhibited size-dependent protein binding in vitro. Urine and ultrafiltrates of plasma were separated by size into narrow fractions using gel permeation chromatography. The sieving coefficient (theta) for ultrafilterable DS of 15A radius averaged 0.68 +/- 0.03 in nonproteinuric vs. 0.95 +/- 0.05 in nephrotic subjects (P < 0.001). Uncharged dextrans of broad size distribution were used to evaluate barrier size-selectivity in separate groups of nonproteinuric subjects (n = 19) and nephrotic patients with either minimal change (n = 20) or membranous nephropathy (n = 27). The value of theta for an uncharged dextran of similarly small radius (approximately 18 A) was significantly larger than that observed for DS in nonproteinuric subjects, but was similar in nephrotic individuals. Further, impaired barrier size-selectivity, as assessed by the sieving profile for uncharged dextrans (18-60 A radius), failed to account fully for the observed level of albuminuria in almost half of the patients with either minimal change (9/20) or membranous nephropathy (12/27). Together these findings suggest that the human glomerular capillary wall normally provides an electrostatic barrier to filtration of negatively charged macromolecules such as albumin, and that impairment of this electrostatic barrier contributes to the magnitude of albuminuria in the nephrotic syndrome.

The structure of an engineered domain-swapped ribonuclease dimer and its implications for the evolution of proteins toward oligomerization.

BACKGROUND: Domain swapping has been proposed as a mechanism that explains the evolution from monomeric to oligomeric proteins. Bovine and human pancreatic ribonucleases are monomers with no biological properties other than their RNA cleavage ability. In contrast, the closely related bovine seminal ribonuclease is a natural domain-swapped dimer that has special biological properties, such as cytotoxicity to tumour cells. Several recombinant ribonuclease variants are domain-swapped dimers, but a structure of this kind has not yet been reported for the human enzyme. RESULTS: The crystal structure at 2 A resolution of an engineered ribonuclease variant called PM8 reveals a new kind of domain-swapped dimer, based on the change of N-terminal domains between the two subunits. The swapping is fastened at both hinge peptides by the newly introduced Gln101, involved in two intermolecular hydrogen bonds and in a stacking interaction between residues of different chains. Two antiparallel salt bridges and water-mediated hydrogen bonds complete a new interface between subunits, while the hinge loop becomes organized in a 3(10) helix structure. CONCLUSIONS: Proteins capable of domain swapping may quickly evolve toward an oligomeric form. As shown in the present structure, a single residue substitution reinforces the quaternary structure by forming an open interface. An evolutionary advantage derived from the new oligomeric state will fix the mutation and favour others, leading to a more extended complementary dimerization surface, until domain swapping is no longer necessary for dimer formation. The newly engineered swapped dimer reported here follows this hypothetical pathway for the rapid evolution of proteins.

Three-dimensional structure of porcine pancreatic procarboxypeptidase A. A comparison of the A and B zymogens and their determinants for inhibition and activation.

The three-dimensional structure of procarboxypeptidase A (PCPA) from porcine pancreas has been determined at 2 A resolution and refined to a crystallographic R-factor of 0.198, with a root-mean-square deviation from ideal values for bond lengths of 0.015 A and for angles of 2.1 degrees. It is compared with procarboxypeptidase B (PCPB) from the same tissue. The 94/95 residue activation segments of PCPA/PCPB have equivalent folds: an N-terminal globular region with an open sandwich antiparallel alpha/antiparallel beta topology, followed by an extended alpha-helical segment, the connection to the enzyme. Alignment of the secondary structures of the activation segments of PCPA and PCPB (residues A1 to A99) indicates a two residue insertion between residues A34 and A35 and a C-terminal helix that is two turns longer in PCPA compared to PCPB. A deletion is observed between residues A43 to A45, the region containing the short 3(10) helix that covers the active site in PCPB. The globular region (A4 to A80) shields the preformed active center of carboxypeptidase A (CPA), but none of the residues involved in catalysis makes direct contacts with the activation segment. In contrast, subsites S2, S3 and S4 of the enzyme, involved in the binding of peptidic substrates, are blocked by specific contacts with residues AspA36, TrpA38, ArgA47, AspA53 and GluA86 of the activation segment. It has been described that several residues of CPA exhibit different conformations in the free enzyme compared to when substrate is bound: Arg127, Arg145, Glu270 and Tyr248. In PCPA all of these residues are found in the "active" conformation, as if substrate were actually bound. The presence of a ligand, tentatively interpreted as a free amino acid (Val) in the active center could explain this fact. The connecting region (A80 to A99), the target for proteolytic activation, establishes fewer contacts with the enzyme in PCPA than in PCPB. The activation segment of PCPA (A4 to A99) remains bound to the enzyme after the first trypsin cleavage between ArgA99-Ala1 probably due to the stability conferred on it by the alpha-helix (alpha 3) of the connecting segment. These and other structural features may explain the differences in intrinsic activity and different rates or proteolytic activation of each zymogen.

Three-dimensional structure of a human pancreatic ribonuclease variant, a step forward in the design of cytotoxic ribonucleases.

We have determined the crystal structure of a human pancreatic ribonuclease or RNase 1 variant at 1.65 A resolution. Five residues in the N-terminal region were substituted by the corresponding amino acids of the bovine seminal RNase. In addition, a Pro to Ser mutation was present at position 50. The substitution of part of the N terminus has been critical both in improving the expression of this enzyme as a recombinant protein and in achieving its crystallisation. The determination of the crystal structure revealed the characteristic RNase fold including a V-shaped beta-sheet and three alpha-helices. It differs from its bovine RNase orthologue mainly in the loop regions. The active-site cleft shows a similar architecture to that of its bovine counterpart, with the essential residues occupying equivalent positions. In the present structure, however, His119 is displaced as it is in the structure of RNase A at high pH. An interaction model of human ribonuclease with the ribonuclease inhibitor, together with inhibition assays, indicate that, in contrast to RNase A, the modification of the loop beta4beta5 is not enough to avoid inhibition. This study represents the first crystallographic approach to the human enzyme, and should constitute an invaluable tool for the design of ribonuclease variants with acquired cytotoxic properties.

Crystallographic analysis reveals the 12-fold symmetry of the bacteriophage phi29 connector particle.

The internal symmetry of the connector or portal particle from the double-stranded DNA bacteriophage phi29 has been examined by X-ray crystallography. This large multimeric structure (420 kDa) is built up by a number of identical subunits of the p10 protein. It connects the head of the virus with the tail and plays a central role in the prohead assembly and DNA packaging. For the first time a bacteriophage connector has been crystallized and X-ray data have been collected up to a resolution of 3.2 A. A self-rotation function has been calculated, unambigously revealing the 12-fold symmetry of the particle and its orientation in the crystal lattice. The orientation has been confirmed by calculating a cross-rotation function using a low resolution model based on electron microscopy reconstructions.

Purification, crystallization and preliminary X-ray diffraction studies of the bacteriophage phi29 connector particle.

The connector or portal particle from double-stranded DNA bacteriophage phi29 has been crystallized. This structure, which connects the head of the virus with the tail and plays a central role in prohead assembly and DNA packaging and translocation, is formed by 12 subunits of the p10 protein and has a molecular weight of 430 kDa. The connector structure was proteolysed with endoproteinase Glu-C from Staphylococcus aureus V8, which removes 13 and 18 amino acids from the amino- and carboxy-terminal regions of the p10 protein, respectively. Two crystal forms were grown from drops containing an alcohol solution and paraffin oil. Crystals of form I are monoclinic, space group C2 with cell dimensions a = 416.86 A, b = 227.62 A, c = 236.68 A and beta = 96.3 degrees and contain four connector particles per asymmetric unit. Crystals of form II are tetragonal, space group P4(2)2(1)2 with cell dimensions a = b = 170.2 A, c = 156.9 A and contain half a particle per asymmetric unit. X-ray diffraction data from both native crystal forms have been collected to 6.0 and 3.2 A respectively, using synchrotron radiation. Crystals of form II are likely to have the same packing arrangement as the two-dimensional crystals analyzed previously by electron microscopy.

The role of 2',3'-cyclic phosphodiesters in the bovine pancreatic ribonuclease A catalysed cleavage of RNA: intermediates or products?

There is a considerable degree of ambiguity in the literature regarding the role of the 2',3'-cyclic phosphodiesters formed during the reaction of RNA cleavage catalysed by ribonuclease. Usually the reaction is considered to take place in two steps: in the first step there is a transphosphorylation of the RNA 3',5'-phosphodiester bond broken yielding a 2',3'-cyclic phosphodiester which in the second step is hydrolysed to a 3'-nucleotide. Although in many occasions, either explicitly or implicitly, the reaction is treated as taking place sequentially, this is not the case as it has been shown that the 2',3'-phosphodiesters are actually released to the medium as true products of the reaction and that no hydrolysis of these cyclic compounds takes place until all the susceptible 3',5'-phosphodiester bonds have been cyclised. Comparison of the hydrolysis and alcoholysis of the 2',3'-phosphodiesters catalysed by RNase A indicates that the hydrolysis reaction has to be considered formally as a special case of the transphosphorylation back reaction in which the R group of the R-OH substrate is just H. It is thus concluded that the 2',3'-cyclic phosphodiesters formed in the ribonuclease A reaction are true products of the transphosphorylation reaction and not intermediates as usually considered.

Towards on line monitoring the evolution of the myocardium infarction scar with an implantable electrical impedance spectrum monitoring system.

The human heart tissue has a limited capacity for regeneration. Tissue and cellular therapies based on the use of stem cells may be useful alternatives to limit the size of myocardial infarction. In this paper, the preliminary results from an experimental campaign for on-line monitoring of myocardium scar infarction are presented. This study has been carried out under a research project that has as main objective the development and application of a bioactive patch implant for regeneration of myocardial infarction. Electrical Impedance Spectroscopy (EIS) has been chosen as a tissue state monitoring technique. What is presented in this communication is the first results of an implantable EIS measurement system which has been implanted in a subset of the animals corresponding to the control group, along one month. In all the animals, the myocardial infarction was induced by the ligation of the first circumflex marginal artery. In the animal group presented, the bioactive patch scaffold and the electrodes were implanted without the stem cells load. The scaffold is a piece of decellularized human pericardium, lyophilized and rehydrated with hydrogel RAD16-I. Nanogold particles were also placed near the electrodes to improve the electrode area conductivity. The results presented correspond to the subset of animals (n = 5), which had implanted the bioimpedance system monitoring the electrical impedance spectrum in vivo during 1 month. Two electrodes were connected to the bioactive patch implant. A total of 14 logarithmically spaced frequencies were measured every 5 minutes, from 100 Hz to 200 kHz. Results show a convergence of low-frequency and high frequency impedance magnitudes along the measurement period, which is coherent with the scar formation.

Transplanting the highly sensitized patient: The emory algorithm.

Renal transplant patients sensitized to HLA antigens comprise nearly one-third of the UNOS wait-list and receive 14% of deceased donor (DD) transplants, a rate half that of unsensitized patients. Between 1999 and 2003, we performed 492 adult renal transplants from DD; 120 patients (approximately 25%) had a panel reactive antibody (PRA) of >30%, with nearly half (n = 58) having a PRA of >80%. Our approach is based upon high-resolution solid-phase HLA antibody analysis to identify class I/II antibodies and a 'virtual crossmatch' to predict compatible donor/recipient combinations. Recipients are excluded from the United Network for Organ Sharing match run if donors possess unacceptable antigens. Thus, when sensitized patients appear on the match run, they have a high probability of a negative final crossmatch. Here, we describe our 5-year experience with this approach. Five-year graft survival ranged from 66% to 70% among unsensitized (n = 272), moderately sensitized (PRA < 30%, n = 100) and highly sensitized (>30% PRA; n = 120) patients, equal to the average national graft survival (65.7%). The application of this approach (the Emory Algorithm) provides a logical and systematic approach to improve the access of sensitized patients to DD organs and promote more equitable allocation to a highly disadvantaged group of patients awaiting renal transplantation.

Early glomerular dysfunction in human renal allografts.

BACKGROUND: The long-term outcome of renal allografts is characterized by a progressive deterioration of renal function and graft loss. Our aim was to determine early glomerular functional abnormalities, before they become clinically apparent. METHODS: Glomerular hemodynamics and dextran sieving were characterized in 21 well-functioning cadaveric renal allograft recipients [normal glomerular filtration rate (GFR) and albumin excretion rate (AER), who also had a kidney biopsy with normal or minimal histological changes] and in 15 uninephrectomized kidney donors. Both groups were one to three years after transplantation or uninephrectomy. RESULTS: The GFR and renal plasma flow (RPF) were similar in both groups (62 +/- 3 vs. 63 +/- 4, and 343 +/- 26 vs. 334 +/- 21 mL/min/1.73 m2 for GFR and RPF, in cadaveric recipients vs. donors, respectively), the AER was normal in both groups, but the mean arterial pressure was higher in renal recipients (103 +/- 3 vs. 94 +/- 3 mm Hg in uninephrectomy controls, P < 0.05). Despite similar levels of overall glomerular function in the two groups, the dextran sieving curve was uniformly elevated in the renal allograft recipients versus uninephrectomy controls (P < 0.05 for dextrans 38 to 66 A). Using a log-normal glomerular pore-size distribution model to analyze potential mechanisms, the elevation in the dextran sieving curve resulted from a shift in the distribution of glomerular filtering pores to a larger size (mean glomerular pore size 46 +/- 2 vs. 43 +/- 2 A for uninephrectomy controls, P < 0.05), resulting in a larger fraction of filtrate volume permeating very large pores. By morphometric analysis, the thickness of the glomerular basement membrane was increased in kidney allograft as compared to 2-kidney biopsy controls (614 +/- 33 vs. 427 +/- 22 nm, respectively, P < 0.05). CONCLUSIONS: Even in "well functioning" renal allografts there is a glomerular dysfunction characterized by increased permeability to macromolecules resulting from a shift of the glomerular pores to a larger size. These changes could be mediated by ultrastructural alterations at the glomerular capillary or by alterations in intraglomerular hemodynamics. Early allograft dysfunction may contribute to the progressive renal insufficiency of renal allografts.

Determinants of glomerular hypofiltration in nephrotic patients with minimal change nephropathy.

Physiologic and morphologic techniques were used to elucidate the determinants of the GFR in 25 nephrotic patients with minimal change nephropathy. They were divided into two groups according to the finding of either a normal (Group 1, N = 13) or a depressed (Group 2, N = 12) inulin clearance. RPF, afferent oncotic pressure, and dextran sieving coefficients were determined. Mathematical models of glomerular ultrafiltration were then used to compute likely upper bounds for the ultrafiltration coefficient and pore area/length ratio (a measure of pore density). The upper bounds for each measure of intrinsic ultrafiltration capacity were depressed below estimated normal values in healthy controls by 55 and 47% in Group 1 patients and by 86 and 83% in Group 2 patients with minimal change nephropathy. A corresponding excess of ultrafiltration pressure (versus control), attributable solely to reduced intracapillary oncotic pressure, was by 10.8 and 11.5 mm Hg, respectively. Glomerular morphometry revealed peripheral capillary filtration surface area to be preserved in both minimal change nephropathy groups. However, a significant reduction in filtration slit frequency due to epithelial podocyte broadening correlated with the computed ultrafiltration coefficient across the two minimal change nephropathy groups (r = 0.65; P < 0.001). It was concluded that podocyte deformation invariably lowers the ultrafiltration coefficient and pore area/length ratio in minimal change nephropathy but that an offsetting reduction in intracapillary oncotic pressure prevents the GFR from declining in many cases. However, the models presented here predict that the depression of capillary oncotic pressure is insufficient to compensate when the ultrafiltration coefficient is lowered by substantially more than half and that it is in this circumstance that minimal change nephropathy is most likely to be accompanied by glomerular hypofiltration.

Mechanisms of proteinuria in nephrotic humans.

The glomerular capillary wall imposes a remarkably efficient barrier to the passage of proteins the size of albumin and larger. The development of heavy proteinuria signifies impairment of the function of this barrier. Because endogenous proteins of graded size are heterogeneous with respect to their molecular charge and undergo extensive tubular reabsorption, they are not useful for quantifying the extent of barrier dysfunction. An alternative approach is to determine the fractional clearance of uncharged and non-reabsorbable polymers of graded size. When combined with a hydrodynamic theory of solute transport through a heteroporous membrane, the intrinsic properties of healthy and diseased glomerular capillary walls can be inferred. This approach reveals the nephrotic range proteinuria that attends minimal change nephropathy to be associated with impairment of both the size- and charge-selective properties of glomerular capillary walls.

Selectivity of the glomerular filtration barrier in healthy and nephrotic humans.

The glomerular capillary wall imposes a remarkably efficient barrier to the passage of proteins the size of albumin and larger. The development of heavy proteinuria signifies impairment in the function of this barrier. Because endogenous proteins of graded size are heterogeneous with respect to their molecular charge, and undergo extensive tubular reabsorption, they are not useful for quantifying the extent of barrier dysfunction. An alternative approach is to determine the fractional clearance of uncharged and nonreabsorbable polymers of graded size. When combined with a hydrodynamic theory of solute transport through a heteroporous membrane, the intrinsic properties of healthy and diseased glomerular capillary walls can be inferred. This approach reveals the nephrotic range proteinuria that attends membranous nephropathy to be associated with impairment of both the size- and charge-selective properties of glomerular capillary walls.

Three-dimensional structure of porcine procarboxypeptidase B: a structural basis of its inactivity.

Procarboxypeptidase B is converted to enzymatically active carboxypeptidase B by limited proteolysis catalysed by trypsin, removing the long N-terminal activation segment of 95 amino acids. The three-dimensional crystal structure of procarboxypeptidase B from porcine pancreas has been determined at 2.3 A resolution and refined to a crystallographic R-factor of 0.169. The functional determinants of its enzymatic inactivity and of its activation by limited proteolysis have thus been unveiled. The activation segment folds in a globular region with an open sandwich antiparallel-alpha antiparallel-beta topology and in a C terminal alpha-helix which connects it to the enzyme moiety. The globular region (A7-A82) shields the preformed active site, and establishes specific interactions with residues important for substrate recognition. AspA41 forms a salt bridge with Arg145, which in active carboxypeptidase binds the C-terminal carboxyl group of substrate molecules. The connecting region occupies the putative extended substrate binding site. The scissile peptide bond cleaved by trypsin during activation is very exposed. Its cleavage leads to the release of the activation segment and to exposure of the substrate binding site. An open-sandwich folding has been observed in a number of other proteins and protein domains. One of them is the C-terminal fragment of L7/L12, a ribosomal protein from Escherichia coli that displays a topology similar to the activation domain of procarboxypeptidase.