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

Autor: Jette S. Kastrup, Bjarne Stoffer, Poul Baad Rasmussen, Anja K. Pedersen, Hans Flodgaard, Lars Fogh Iversen, Søren E. Bjørn, Viggo Linde, Ingrid Kjøller Larsen
Rok vydání: 2001
Předmět:
Zdroj: Proteins: Structure, Function, and Bioinformatics. 42:442-451
ISSN: 0887-3585
DOI: 10.1002/1097-0134(20010301)42:4<442::aid-prot30>3.0.co;2-s
Popis: 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.
Databáze: OpenAIRE
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