[Surgery of peritoneal surface malignancies - surgical cytoreduction and hyperthermic intraperitoneal chemotherapy]. / A peritoneális felszín tumorainak sebészete ­ citoreduktív sebészet és hipertermiás intraperitoneális kemoterápia.

Peritoneal carcinosis has historically been considered as inoperable, although the technique of its resesection together with high dose intraperitoneal chemotherapy potentiated by heat has been described decades ago. It has not became a widely practiced routine except in specialized centers - the complex technique, weakly standardized but resource demanding chemotherapy, lacking financial background and the many times questionable clinical benefit at a cost of high surgical load might have been the key factors. Refined technology, developing chemotherapy protocols together with growing clinical evidence are now more sharply delineating the range of indications where the procedure might be beneficial, increases survival, or is the only curative therapy. These include tumors of the appendix and pseudomyxoma peritonei, mesothelioma, and selected cases of ovarian, colorectal and gastric cancer. In addition to technical description of the intervention, we summarize the currently valid indications and describe our institutional protocol for the treatment of appendiceal malignancies.

Serum fetuin-A is decreased in cirrhotic patients with Wilson's disease.

INTRODUCTION: Wilson's disease may lead to cirrhosis, but timely medical treatment could slow down its progression. Clinical markers helping early diagnosis are essential. Decreased fetuin-A concentration has been reported in cirrhosis of different etiologies. The aim of this study was to investigate whether decreased serum fetuin-A concentration could identify patients with Wilson's disease who developed cirrhosis. MATERIALS AND METHODS: In this cross-sectional study we determined the serum fetuin-A concentration of 50 patients with Wilson's disease. We analyzed the data of patients with liver involvement, comparing cirrhotic and non-cirrhotic patients. RESULTS: Among patients with liver involvement those with cirrhosis had significantly lower fetuin-A and albumin level, white blood cell and platelet count. Fetuin-A negatively correlated with disease duration, bilirubin level, positively with total protein and albumin concentration, but not with copper and ceruloplasmin concentrations or markers of systemic inflammation. In multivariate analysis with fetuin-A and the Nazer score or its parameters only fetuin-A was a significant determinant of having cirrhosis. In receiver operator curve analysis among patients with liver involvement the fetuin-A level of 523 µg/ml was associated with cirrhosis with 82% sensitivity and 87% specificity. The presence of the H1069Q mutation was not associated with alteration in fetuin-A concentration. CONCLUSIONS: The serum concentration of fetuin-A is a sensitive marker of liver cirrhosis in Wilson's disease, independently of the H1069Q mutation, ceruloplasmin concentration or systemic inflammation.

High serum Hsp70 level predicts poor survival in colorectal cancer: Results obtained in an independent validation cohort.

BACKGROUND: Hsp70 plays important role in the development and progression of cancer. Previously we described the association between serum Hsp70 levels and mortality of colorectal cancer. OBJECTIVE: In this new prospective study we aimed to confirm and extend our previous findings in a larger cohort of patients, based on a longer follow-up period. METHODS: Two hundred and thirty-two patients diagnosed with colorectal cancer were enrolled in the study. Baseline serum Hsp70 level and classical biomarker levels were measured. Patients were treated according to stage of the tumor and follow-up lasted for a median 46.4 months. RESULTS: We found that serum Hsp70 concentrations increase significantly with stage of the disease (1.79; 2.23 and 3.21 ng/ml in stage I+II, III and IV respectively, p= 0.012 and 0.002, Mann-Whitney test) and with other known biomarkers of the disease. We managed to confirm our previous findings that high baseline serum Hsp70 level (> 1.64 ng/ml) predicted poor 5-year survival (risk of death HR: 1.94 CI: 1.294-2.909; univariate; HR: 2.418 CI: 1.373-4.258; multivariate Cox regression analysis) in the whole patient population and also in subgroups of stage IV and stage III disease. The strongest association was observed in women under age of 70 (HR: 8.12, CI: 2.02-35.84; p= 0.004; multivariate Cox regression). The power of this colorectal cancer prognostic model could be amplified by combining Hsp70 levels and inflammatory markers. Patients with high Hsp70, CRP and high baseline WBC or platelet count had 5-times higher risk of death (HR: 5.07 CI: 2.74-9.39, p< 0.0001; and HR: 4.98 CI: 3.08-8.06, p< 0.0001 respectively). CONCLUSIONS: These results confirm and validate our previous findings that serum Hsp70 is a useful biomarker of colorectal cancer.

Platelet Count, ADAMTS13 Activity, von Willebrand Factor Level and Survival in Patients with Colorectal Cancer: 5-Year Follow-up Study.

Distant metastasis is a major cause of colorectal cancer-related death, but the mechanism of tumour progression is not fully understood. There is growing evidence of an interaction between tumour cells and platelets which may influence tumour progression and metastasis formation. Quality and quantity of von Willebrand factor may regulate the interaction between tumour cells and platelets. Our aim was to measure the platelet count, von Willebrand factor antigen (VWF:Ag) levels and ADAMTS13 activity in a large (n = 232) cohort of colorectal cancer patients and to examine their relationships with the stage of the disease and 5-year survival without thrombotic complications using multivariable models. Significantly higher platelet counts (p = 0.005), VWF:Ag levels (p = 0.008) and decreased ADAMTS13 activity (p = 0.006) were observed in patients with metastatic disease. Results of the Kaplan-Meier analysis showed that lower platelet counts (p < 0.0001), lower VWF:Ag (p = 0.0008) levels and higher ADAMTS13 activity (p < 0.0001) were associated with better event-free survival. Finally, to investigate the association between overall event-free survival and the three study variables, multivariate Cox proportional hazard models were generated. All models were adjusted for age, gender and disease stage. Platelet count, ADAMTS13 activity or VWF:Ag level were incorporated and all of these variables turned out to be age-, gender- and stage-independent predictors of mortality (all hazard ratio >1.7, p < 0.05). In summary, this is the first observational study reporting association between higher mortality or thrombotic complications and increased platelet count, increased VWF:Ag levels and decreased ADAMTS13 activity in colorectal cancer.

Circulating mitochondrial stress 70 protein/mortalin and cytosolic Hsp70 in blood: Risk indicators in colorectal cancer.

Mitochondrial mortalin and cytosolic Hsp70 are essential chaperones overexpressed in cancer cells. Our goals were to reproduce our earlier findings of elevated circulating levels of mortalin and Hsp70 in colorectal cancer (CRC) patients with a larger patient cohort, to compare death risk assessment of mortalin, Hsp70, CEA and C19-9 and to assess their prognostic value in various CRC stages. Mortalin, Hsp70, CEA and CA19-9 levels were determined in sera of 235 CRC patients enrolled in the study and followed up 5 years after surgery. Association between their concentrations and patients' survival was analyzed by Kaplan-Meier estimator and subjected to Cox Proportional hazards analysis. Serum level of mortalin was independent of that of Hsp70, CEA and CA19-9, whereas Hsp70 level weakly correlated with CEA and CA19-9 levels. Improved short-term survival was found in early or advanced disease stages associated with lower mortalin and Hsp70 levels. Cox regression analysis showed a high mortality hazard (HR = 3.7, p < 0.001) in patients with both high mortalin and Hsp70 circulating levels. Multivariate analysis showed that high mortalin and Hsp70 significantly enhances risk score over a baseline model of age, number of affected lymph nodes, CEA, CA19-9, disease stage and perioperative therapy. Analysis of mortalin and Hsp70 in CRC patients' sera adds a high prognostic value to TNM stage and to CEA and CA19-9 and identifies patients with lower or higher survival probability in all CRC stages. Determination of mortalin and Hsp70 in blood could be a useful additive prognostic tool in guiding clinical management of patients.

The role of structural flexibility and stability in the interaction of serine proteases with their inhibitors.

Serine proteases and their natural inhibitors have long been served as excellent models for studying (primary, secondary and tertiary) structure - activity relationships of biologically interacting proteins. As protein flexibility has been accepted as a "fourth dimension" of the protein structure, its contribution to the binding process has gained much interest. In this article we review extreme cases of serine protease interactions with canonical serine protease inhibitors that provide unique insights into the dynamics of protein- protein interactions. The major conclusions of our review article are: a) taxon-specific inhibitory effects of two highly homologous protease inhibitors from Schistocerca gregaria (SGCI and SGTI), as investigated by H/D exchange experiments and NMR spectroscopy, are due to their differential flexibilities, b) stabilities of some protease and inhibitor complexes, the wide-spread and increased flexibility of some segments in the protein-protein complexes, as studied by X-ray crystallography and NMR-spectroscopy, appear to be proportional to the physical stability of the complex.

Biochemical characterisation of chymotrypsin from the midgut gland of yellowleg shrimp, Penaeus californiensis.

Chymotrypsin from shrimp, Penaeus californiensis, was compared to Bos taurus chymotrypsin, and its structure-function relationship was studied. Catalytic efficiency toward synthetic substrate is lower, but it has a broad specificity and higher activity toward protein substrates, including collagen. It is active at pH 4-10 and fully active up to 50 °C for 2 h and at least nine days at room temperature. The activation peptide is twice as long as bovine chymotrypsinogen, has less disulfide bridges, and is a single polypeptide. Only one activation step is necessary from chymotrypsinogen to the mature enzyme. Postmortem implications in muscle softening and melanisation, resistance to temperature and pH and efficiency with proteinaceous substrates make chymotrypsin useful as a biotechnological tool in food processing. This makes shrimp processing wastes useful as a material for production of fine reagents.

Isolation and characterization of a protease inhibitor from Acacia karroo with a common combining loop and overlapping binding sites for chymotrypsin and trypsin.

By using affinity and reversed-phase HPLC (RP-HPLC) chromatographies two chymotrypsin-trypsin inhibitors were isolated from seeds of Acacia karroo, a legume of the subfamily Mimosoideae. The primary structure of one of these inhibitors, named AkCI/1, was determined. The inhibitor consists of two polypeptide chains, 139 and 44 residues respectively, which are linked by a single disulfide bridge. The amino acid sequence of AkCI/1 is homologous to and showed more than 60% sequence similarity with other protease inhibitors isolated earlier from the group of Mimosoideae. AkCI/1 inhibits both chymotrypsin (EC 3.4.21.1) and trypsin (EC 3.4.21.4) in a 1:1M ratio with Ki values of 2.8 × 10(-12)M and 1.87 × 10(-12)M, respectively. The P1-P1' residues for trypsin were identified as Arg68-Ile69 by selective hydrolysis of the inhibitor at this site, with bovine trypsin and human trypsin IV. The cleavage did not affect the inhibition of trypsin, but fully abolished the chymotrypsin inhibitory activity of AkCI/1. This finding together with our studies on competition of the two enzymes for the same combining loop suggests that the same loop has to contain the binding sites for both proteases. The most likely P1 residue of AkCI/1 for chymotrypsin is Tyr67.

Metastasis blood test by flow cytometry: in vivo cancer spheroids and the role of hypoxia.

Cancer hypoxia correlates with therapeutic resistance and metastasis, suggesting that hypoxic adaptation is a critical survival advantage for cancer stem cells (CSCs). Hypoxic metabolism, however, may be a disadvantage in aerobic circulation as the extremely low incidence of metastasis-compared to the high circulating tumor-cell numbers (CTCs)-appears to suggest. As rare metastatic CSCs still survive, we searched for a mechanism that protects them from oxygen in circulation. CSCs form multicellular spheroids in vitro from virtually all cancers tested. We asked, therefore, whether cancers also form spheroids in vivo and whether circulating spheroids play a role in metastasis. We used metabolic, apoptotic and hypoxia assays, we measured aerobic barriers and calculated hypoxia vs. spheroid-size correlations. We detected metabolic/oxidative stress in spheroids, we found correlation between stem cell presence and hypoxia and we showed that the size of hypoxic spheroids is compatible with circulation. To detect spheroids in patients, we worked out a new light-scatter flow cytometry blood test and assayed 67 metastatic and control cases. We found in vivo spheroids with positive stem cell markers in cancer blood and they showed exclusive correlation with metastasis. In conclusion, our data suggest that metastatic success depends on CSC-association with in vivo spheroids. We propose that the mechanism involves a portable "micro-niche" in spheroids that may support CSC-survival/adaptation in circulation. The new assay may establish a potential early marker of metastatic progression.

Biochemical characterization of Acacia schweinfurthii serine proteinase inhibitor.

One of the many control mechanisms of serine proteinases is their specific inhibition by protein proteinase inhibitors. An extract of Acacia schweinfurthii was screened for potential serine proteinase inhibition. It was successfully purified to homogeneity by precipitating with 80% (v/v) acetone and sequential chromatographic steps, including ion-exchange, affinity purification and reversed-phase high performance liquid chromatography. Reducing sodium dodecyl sulphate polyacrylamide gel electrophoresis conditions revealed an inhibitor (ASTI) consisting of two polypeptide chains A and B of approximate molecular weights of 16 and 10 kDa, respectively, and under non-reducing conditions, 26 kDa was observed. The inhibitor was shown to inhibit bovine trypsin (Ki of 3.45 nM) at an approximate molar ratio of inhibitor:trypsin (1:1). The A- and B-chains revealed complete sequences of 140 and 40 amino acid residues, respectively. Sequence similarity (70%) was reported between ASTI A-chain and ACTI A-chain (Acacia confusa) using ClustalW. The B-chain produced a 76% sequence similarity between ASTI and Leucaena leucocephala trypsin inhibitor.

Comparison of complexes formed by a crustacean and a vertebrate trypsin with bovine pancreatic trypsin inhibitor - the key to achieving extreme stability?

This paper provides evidence for the extremely high resistance of a complex of crayfish trypsin (CFT) and bovine pancreatic trypsin inhibitor (BPTI) against heating and chemical denaturing agents such as sodium dodecyl sulfate (SDS) and urea. To dissociate this complex, 15 min boiling in SDS was necessary, compared to a complex of bovine trypsin (BT) (EC 3.4.21.4) and BPTI, which dissociates in SDS without boiling. The CFT-BPTI complex remained stable even in 9 m urea, while the BT-BPTI complex started to dissociate at concentrations of approximately 4 m urea. The melting temperatures of the BT-BPTI and CFT-BPTI complexes, as determined by differential scanning calorimetry, were found to be 79.6 and 100.1 °C, respectively. The behaviour of the apo-enzymes - CFT was found to have a less stable structure compared to BT - did not provide a definite indication regarding the differential effects on their stabilities. To explore the structural features responsible for this extreme stability, we crystallized CFT in complex with BPTI, and identified extended contacts compared to the BT-BPTI complex. Comparison of the B-factors of similar trypsin-trypsin inhibitor complexes suggests that molecular flexibility of the components is also required for the strong protein-protein interaction. Although the structural reason for the extreme stability of the CFT-BPTI complex is not yet fully understood, our study may be a starting point for the development of new protein complexes with enhanced stability.

Internal friction in enzyme reactions.

The empirical concept of internal friction was introduced 20 years ago. This review summarizes the results of experimental and theoretical studies that help to uncover the nature of internal friction. After the history of the concept, we describe the experimental challenges in measuring and interpreting internal friction based on the viscosity dependence of enzyme reactions. We also present speculations about the structural background of this viscosity dependence. Finally, some models about the relationship between the energy landscape and internal friction are outlined. Alternative concepts regarding the viscosity dependence of enzyme reactions are also discussed.

Temperature dependence of internal friction in enzyme reactions.

Our aim was to elucidate the physical background of internal friction of enzyme reactions by investigating the temperature dependence of internal viscosity. By rapid transient kinetic methods, we directly measured the rate constant of trypsin 4 activation, which is an interdomain conformational rearrangement, as a function of temperature and solvent viscosity. We found that the apparent internal viscosity shows an Arrhenius-like temperature dependence, which can be characterized by the activation energy of internal friction. Glycine and alanine mutations were introduced at a single position of the hinge of the interdomain region to evaluate how the flexibility of the hinge affects internal friction. We found that the apparent activation energies of the conformational change and the internal friction are interconvertible parameters depending on the protein flexibility. The more flexible a protein was, the greater proportion of the total activation energy of the reaction was observed as the apparent activation energy of internal friction. Based on the coupling of the internal and external movements of the protein during its conformational change, we constructed a model that quantitatively relates activation energy, internal friction, and protein flexibility.

Reversible heat-induced dissociation of ß2-microglobulin amyloid fibrils.

Recent progress in the field of amyloid research indicates that the classical view of amyloid fibrils, being irreversibly formed highly stable structures resistant to perturbating conditions and proteolytic digestion, is getting more complex. We studied the thermal stability and heat-induced depolymerization of amyloid fibrils of ß(2)-microglobulin (ß2m), a protein responsible for dialysis-related amyloidosis. We found that freshly polymerized ß2m fibrils at 0.1-0.3 mg/mL concentration completely dissociated to monomers upon 10 min incubation at 99 °C. Fibril depolymerization was followed by thioflavin-T fluorescence and circular dichroism spectroscopy at various temperatures. Dissociation of ß2m fibrils was found to be a reversible and dynamic process reaching equilibrium between fibrils and monomers within minutes. Repolymerization experiments revealed that the number of extendable fibril ends increased significantly upon incubation at elevated temperatures suggesting that the mechanism of fibril unfolding involves two distinct processes: (1) dissociation of monomers from the fibril ends and (2) the breakage of fibrils. The breakage of fibrils may be an important in vivo factor multiplying the number of fibril nuclei and thus affecting the onset and progress of disease. We investigated the effects of some additives and different factors on the stability of amyloid fibrils. Sample aging increased the thermal stability of ß2m fibril solution. 0.5 mM SDS completely prevented ß2m fibrils from dissociation up to the applied highest temperature of 99 °C. The generality of our findings was proved on fibrils of K3 peptide and α-synuclein. Our simple method may also be beneficial for screening and developing amyloid-active compounds for therapeutic purposes.

Serum fetuin-A in metabolic and inflammatory pathways in patients with myocardial infarction.

BACKGROUND: Although multifunctional glycoprotein α2HS-glycoprotein/human fetuin-A (AHSG) is involved in atherosclerosis, it is not clear whether high or low concentrations are more important. We studied the correlation of serum AHSG with adiponectin, leptin, resistin, C-reactive protein (CRP) and tumour necrosis factor-α (TNF-α) to see whether its metabolic effects or its involvement in subclinical inflammation are dominant in patients with established coronary disease. MATERIALS AND METHODS: In this cross-sectional study, AHSG concentration was determined in sera of 171 patients (age: 62 ± 6 years, mean ± SD) with previous myocardial STEMI infarction and normal renal function and 81 age-matched healthy controls by radial immunodiffusion. Results Patients had increased AHSG levels (673 ± 103 vs. 619 ± 96 mg L(-1), P < 0·001) compared to controls. Obese and diabetic patients had higher AHSG concentration than those with normal BMI or without diabetes but even the latter group had elevated AHSG levels (667 ± 101 mg L(-1), n = 88) compared to controls (P = 0·002). Serum AHSG correlated negatively with adiponectin (r = -0·236, P = 0·006) even after adjusting for BMI (r = -0·177, P = 0·043). AHSG determined adiponectin levels independently from BMI, age and other adipocytokines (P = 0·014). The correlation between leptin and AHSG (r = 0·321, P = 0·021) weakened following adjustment for BMI (r = 0·209, P = 0·072). Serum AHSG did not correlate significantly with CRP, resistin and TNF-α concentrations. BMI and resistin but not AHSG determined TNF-α levels independently. CONCLUSIONS: AHSG is elevated in sera of patients with previous myocardial infarction. Association with adipokines favours the concept that AHSG is involved in atherosclerosis more likely through metabolic pathways (insulin resistance, obesity and adipocyte dysfunction) than by inflammation in patients with post-myocardial infarction.

The catalytic aspartate is protonated in the Michaelis complex formed between trypsin and an in vitro evolved substrate-like inhibitor: a refined mechanism of serine protease action.

The mechanism of serine proteases prominently illustrates how charged amino acid residues and proton transfer events facilitate enzyme catalysis. Here we present an ultrahigh resolution (0.93 Å) x-ray structure of a complex formed between trypsin and a canonical inhibitor acting through a substrate-like mechanism. The electron density indicates the protonation state of all catalytic residues where the catalytic histidine is, as expected, in its neutral state prior to the acylation step by the catalytic serine. The carboxyl group of the catalytic aspartate displays an asymmetric electron density so that the O(δ2)-C(γ) bond appears to be a double bond, with O(δ2) involved in a hydrogen bond to His-57 and Ser-214. Only when Asp-102 is protonated on O(δ1) atom could a density functional theory simulation reproduce the observed electron density. The presence of a putative hydrogen atom is also confirmed by a residual mF(obs) - DF(calc) density above 2.5 σ next to O(δ1). As a possible functional role for the neutral aspartate in the active site, we propose that in the substrate-bound form, the neutral aspartate residue helps to keep the pK(a) of the histidine sufficiently low, in the active neutral form. When the histidine receives a proton during the catalytic cycle, the aspartate becomes simultaneously negatively charged, providing additional stabilization for the protonated histidine and indirectly to the tetrahedral intermediate. This novel proposal unifies the seemingly conflicting experimental observations, which were previously seen as either supporting the charge relay mechanism or the neutral pK(a) histidine theory.

Isolation, biochemical characterization, and molecular modeling of American lobster digestive cathepsin D1.

An aspartic proteinase was isolated from American lobster gastric fluid. The purified cathepsin D runs as a single band on native-PAGE displaying proteolytic activity on a zymogram at pH 3.0, with an isoelectric point of 4.7. Appearance of the protein in SDS-PAGE, depended on the conditions of the gel electrophoresis. SDS treatment by itself was not able to fully unfold the protein. Thus, in SDS-PAGE the protein appeared to be heterogeneous. A few minute of boiling the sample in the presence of SDS was necessary to fully denature the protein that then run in the gel as a single band of ~50 kDa. The protein sequence of lobster cathepsin D1, as deduced from its mRNA sequence, lacks a 'polyproline loop' and ß-hairpin, which are characteristic of some of its structural homologues. A comparison of amino acid sequences of digestive and non-digestive cathepsin D-like enzymes from invertebrates showed that most cathepsin D enzymes involved in food digestion, lack the polyproline loop, whereas all non-digestive cathepsin Ds, including the American lobster cathepsin D2 paralog, contain the polyproline loop. We propose that the absence or presence of this loop may be characteristic of digestive and non-digestive aspartic proteinases, respectively.

Anoxia leads to a rapid translocation of human trypsinogen 4 to the plasma membrane of cultured astrocytes.

Trypsinogen 4 is specifically expressed in the human brain, mainly by astroglial cells. Although its exact role in the nervous tissue is yet unclear, trypsin 4-mediated pathological processes were suggested in Alzheimer's disease, multiple sclerosis and ischemic injury. In the present study, we analyzed the intracellular distribution of fluorescently tagged human trypsinogen 4 isoforms during normal and anoxic conditions in transfected mouse primary astrocytes. Our results show that initiation of anoxic milieu by the combined action of KCN treatment and glucose deprivation rapidly leads to the association of leader peptide containing trypsinogen 4 constructs to the plasma membrane. Using rhodamine 110 bis-(CBZ-L-isoleucyl-L-prolyl-L-arginine amide), a synthetic chromogen peptide substrate of trypsin, we show that anoxia can promote extracellular activation of trypsinogen 4 indicating that extracellular activation of human trypsinogen 4 can be an important component in neuropathological changes of the injured human brain.

Mechanism of lysophosphatidic acid-induced amyloid fibril formation of beta(2)-microglobulin in vitro under physiological conditions.

Beta(2)-microglobulin- (beta2m-) based fibril deposition is the key symptom in dialysis-related amyloidosis. beta2m readily forms amyloid fibrils in vitro at pH 2.5. However, it is not well understood which factors promote this process in vivo, because beta2m cannot polymerize at neutral pH without additives even at elevated concentration. Here we show that lysophosphatidic acid (LPA), an in vivo occurring lysophospholipid mediator, promotes amyloid formation under physiological conditions through a complex mechanism. In the presence of LPA, at and above its critical micelle concentration, native beta2m became sensitive to limited proteolytic digestion, indicating increased conformational flexibility. Isothermal titration calorimetry indicates that beta2m exhibits high affinity for LPA. Fluorescence and CD spectroscopy, as well as calorimetry, showed that LPA destabilizes the structure of monomeric beta2m inducing a partially unfolded form. This intermediate is capable of fibril extension in a nucleation-dependent manner. Our findings also indicate that the molecular organization of fibrils formed under physiological conditions differs from that of fibrils formed at pH 2.5. Fibrils grown in the presence of LPA depolymerize very slowly in the absence of LPA; moreover, LPA stabilizes the fibrils even below its critical micelle concentration. Neither the amyloidogenic nor the fibril-stabilizing effects of LPA were mimicked by its structural and functional lysophospholipid analogues, showing its selectivity. On the basis of our findings and the observed increase in blood LPA levels in dialysis patients, we suggest that the interaction of LPA with beta2m might contribute to the pathomechanism of dialysis-related amyloidosis.

Probing conformational plasticity of the activation domain of trypsin: the role of glycine hinges.

Trypsin-like serine proteases play essential roles in diverse physiological processes such as hemostasis, apoptosis, signal transduction, reproduction, immune response, matrix remodeling, development, and differentiation. All of these proteases share an intriguing activation mechanism that involves the transition of an unfolded domain (activation domain) of the zymogen to a folded one in the active enzyme. During this conformational change, activation domain segments move around highly conserved glycine hinges. In the present study, hinge glycines were replaced by alanine residues via site directed mutagenesis. The effects of these mutations on the interconversion of the zymogen-like and active conformations as well as on catalytic activity were studied. Mutant trypsins showed zymogen-like structures to varying extents characterized by increased flexibility of some activation domain segments, a more accessible N-terminus and a deformed substrate binding site. Our results suggest that the trypsinogen to trypsin transition is hindered by the mutations, which results in a shift of the equilibrium between the inactive zymogen-like and active enzyme conformations toward the inactive state. Our data also showed, however, that the inactive conformations of the various mutants differ from each other. Binding of substrate analogues shifted the conformational equilibrium toward the active enzyme since inhibited forms of the trypsin mutants showed similar structural features as the wild-type enzyme. The catalytic activity of the mutants correlated with the proper conformation of the active site, which could be supported by varying conformations of the N-terminus and the autolysis loop. Transient kinetic measurements confirmed the existence of an inactive to active conformational transition occurring prior to substrate binding.