Two mutants of human heparin binding protein (CAP37): toward the understanding of the nature of lipid A/LPS and BPTI binding.

Heparin binding protein (HBP) is an inactive serine protease homologue with important implications in host defense during infections and inflammations. Two mutants of human HBP, [R23S,F25E]HBP and [G175Q]HBP, have been produced to investigate structure-function relationships of residues in the putative lipid A/lipopolysaccharide (LPS) binding site and BPTI (bovine pancreatic trypsin inhibitor) binding site. The X-ray structures have been determined at 1.9 A resolution for [G175Q]HBP and at 2.5 A resolution for the [R23S,F25E]HBP mutant, and the structures have been fully refined to R-factors of 18.2 % and 20.7 %, respectively. The G175Q mutation does not alter the overall structure of the protein, but the ability to bind BPTI has been eliminated, and the mutant mediates only a limited stimulation of the LPS-induced cytokine release from human monocytes. The lipid A/LPS binding property of [G175Q]HBP is comparable with that of native HBP. The R23S,F25E mutations do not affect the binding of lipid A/LPS and BPTI or the LPS-induced cytokine release from human monocytes. This shows that two diverse ligands, lipid A/LPS and BPTI, do not share binding sites. Previously, there was convincing evidence for the proposed lipid A/LPS binding site of HBP. Unexpectedly, the extensive structural changes introduced by mutation of Arg23 and Phe25 do not affect the binding of lipid A/LPS, indicating that another not yet identified site on HBP is involved in the binding of lipid A/LPS.

Heparin-binding protein decreases apoptosis in human and murine neutrophils.

BACKGROUND: Heparin-binding protein (HBP), a serine protease without any known proteolytic activity, is found in human polymorphonuclear leukocyte (PMN) granules, but not in mice. HBP potentiates the endotoxin-induced release of tumor necrosis factor (TNF) alpha, interleukin (IL)-1, and IL-6 from isolated monocytes. HBP has also been shown to increase the survival of cultured monocytes and protect them from oxidative stress. However, whether HBP affects PMNs themselves is not known. MATERIALS AND METHODS: Based on our work with cultured monocytes and the survival benefit noted in experimental peritonitis, we hypothesized that HBP would have a beneficial effect on the survival of neutrophils. We evaluated the effect of HBP on apoptosis in murine peritoneal exudative cells elicited by intraperitoneal thioglycollate administration and in normal human neutrophils from volunteers. Leukocytes were isolated from the peritoneal cavity and blood of mice that underwent intraperitoneal thioglycollate instillation. The mouse peritoneal exudate cells and normal human neutrophils isolated from peripheral blood were used to study the effect of HBP on survival and apoptosis. RESULTS: HBP decreased percentage apoptosis of mouse cells in both serum-enriched (from 24.8 to 4.5%) and serum-deprived (from 23.1 to 8.2%) cultures. In human PMNs, the protective effect of HBP was seen only in the serum-deprived group, with a decrease in percentage apoptosis from 69.1 to 43.3%. CONCLUSIONS: For the first time, we have shown that HBP, in addition to its known augmentation of the proinflammatory response of monocytes, also acts as a prosurvival protein for neutrophils themselves, and thereby enhances local host defense.

Structure and function of the N-linked glycans of HBP/CAP37/azurocidin: crystal structure determination and biological characterization of nonglycosylated HBP.

The three N-glycosylation sites of human heparin binding protein (HBP) have been mutated to produce a nonglycosylated HBP (ng-HBP) mutant. ng-HBP has been crystallized and tested for biological activity. Complete X-ray data have been collected to 2.1 A resolution, and the structure has been fully refined to an R-factor of 18.4% (R(free) 27.7%). The ng-HBP structure reveals that neither the secondary nor tertiary structure have changed due to the removal of the glycosylation, as compared to the previously determined glycosylated HBP structure. Although the primary events in N-linked glycosylation occurs concomitant with polypeptide synthesis and therefore possesses the ability to influence early events in protein folding, we see no evidence of glycosylation influencing the structure of the protein. The root-mean-square deviation between the superimposed structures was 0.24 A (on C alpha atoms), and only minor local structural differences are observed. Also, the overall stability of the protein seems to be unaffected by glycosylation, as judged by the B-factors derived from the two X-ray structures. The flexibility of a glycan site may be determined by the local polypeptide sequence and structure rather than the glycan itself. The biological in vitro activity assay data show that ng-HBP, contrary to glycosylated HBP, mediates only a very limited stimulation of the lipopolysaccharide induced cytokine release from human monocytes. In animal models of fecal peritonitis, glycosylated HBP treatment rescues mice from and an otherwise lethal injury. It appears that ng-HBP have significant effect on survival, and it can be concluded that ng-HBP can stimulate the host defence machinery albeit to a lesser extent than glycosylated HBP.

Atomic resolution structure of human HBP/CAP37/azurocidin.

Crystals of human heparin binding protein (HBP) diffract to 1.1 A when flash-frozen at 120 K. The atomic resolution structure has been refined anisotropically using SHELXL96. The final model of HBP consists of 221 amino-acid residues of 225 possible, three glycosylation units, one chloride ion, 15 precipitant ethanol molecules and 323 water molecules. The structure is refined to a final crystallographic R factor of 15.9% and Rfree(5%) of 18.9% using all data. A putative protein kinase C activation site has been identified, involving residues 113-120. The structure is compared to the previously determined 2.3 A resolution structure of HBP.

Structure of HBP, a multifunctional protein with a serine proteinase fold.

The structure of human heparin binding protein reveals that the serine proteinase fold has been used as a scaffold for a multifunctional protein with antibacterial activity, monocyte and t-cell activating properties and endotoxin and heparin binding capacity.

Crystallization and molecular replacement solution of human heparin binding protein.

The highly glycosylated protein, human heparin binding protein, has been crystallized in the primitive orthorhombic space group P2(1)2(1)2(1) with cell dimensions a = 39.0, b = 66.2 and c = 101.4 A. Ethanol was used as precipitant and glycerol as additive. A full data set has been collected to 3.1 A and diffraction was observed to at least 2.3 A. A molecular replacement solution using human neutrophile elastase as a search model was obtained, showing one molecule per asymmetric unit. The crystal packing showed no bad contacts and the R factor was 44.8% after ten cycles of rigid-body refinement.

Diabetic late complications: will aldose reductase inhibitors or inhibitors of advanced glycosylation endproduct formation hold promise?

Patients suffering from the severe complications associated with both insulin- (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM): nephropathy, retinopathy, neuropathy, and atherosclerosis are still largely left without a prospect of an efficient treatment. This is the case even if it has been assumed for decades and now finally proved by the results from the Diabetes Control and Complications Trial (DCCT) that hyperglycemia is the single main cause of these complications. Improved glycemic control as a result of intensive insulin treatment has the potential to reduce the incidence and progression of complications, but implementation and monitoring of improved glycemic control in all groups of IDDM and NIDDM patients in different communities will be difficult and expensive. Results from the recently terminated DCCT have shown that even with intensive insulin treatment, there will be a significant burden of complications on the diabetic population. It will, therefore, still be of immense importance for the long-term quality of life for the diabetic patient that additional possibilities are developed for prevention and intervention against diabetic complications. Almost two decades of research, animal model testing, and clinical trials have been conducted on various efficient aldose reductase inhibitors. Now the concept of inhibition of formation of advanced glycosylation endproducts on proteins and lipids resulting from extra- and intracellular hyperglycemia is entering the scene as an alternative or perhaps supplementary approach to reduce the occurrence of diabetic complications. An overview of the results from these two fields of research and associated drug-development programs will be presented along with thoughts on possible future developments.

Binding of low molecular weight heparin (Tinzaparin sodium) to bovine endothelial cells in vitro.

Heparinase depolymerized low molecular weight (LMW) heparin (Tinzaparin sodium, Logiparin) was radiolabelled by catalytic tritiation to high specific radioactivity and the binding to fetal bovine heart endothelial (FBHE) cells was studied at 4 degrees C and 37 degrees C. The binding was found to be time dependent and saturable. Two classes of binding sites could be distinguished from Scatchard analysis at both temperatures: One with high affinity (KD = 0.027 microM at 4 degrees C, KD = 0.012 microM at 37 degrees C) and another with very low affinity (KD = 69 microM at 4 degrees C and 37 microM at 37 degrees C). The binding reversibility was affected by the temperature indicating internalization of a fraction of the bound LMW heparin. At 4 degrees C only 11% of the specifically bound heparin was bound irreversibly. At 37 degrees C the non displaceable fraction accounted for 28% of the specifically bound LMW heparin. This work demonstrates that tinzaparin sodium binds specifically to endothelial cells. This binding may be useful in interpreting pharmacokinetic properties of this low molecular weight heparin.