Structure and Assembly of the Catalytic Region of Human Complement Protease C1̄r: A Three-Dimensional Model Based on Chemical Cross-Linking and Homology Modeling
- 1 May 1997
- journal article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 36 (21), 6270-6282
- https://doi.org/10.1021/bi962719i
Abstract
C1r is the modular serine protease responsible for autocatalytic activation of C1, the first component of the complement classical pathway. Its catalytic region is a noncovalent homodimer of two γ-B monomers, each comprising two contiguous complement control protein (CCP) modules, IV and V [also known as short consensus repeats (SCRs)], a 15-residue intermediary segment, and the serine protease B domain. With a view to gain insight into domain−domain interactions within this region, fragment C1̄r (γ-B)2, obtained by autolytic proteolysis of the active protease, was cross-linked with the water-soluble reagent 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide. Cross-linked species γ-B intra and γ-B inter, containing intra- and intermonomer cross-links, respectively, were isolated and then fragmented by CNBr cleavage and trypsin digestion. N-Terminal sequence and mass spectrometry analyses of the resulting cross-linked peptides allowed us to identify one intramonomer cross-link between Lys426 of module V and the C-terminal Asp688 of the serine protease B domain and one intermonomer cross-link between the N-terminal Gly280 of fragment γ and Glu493 of the B domain. Three-dimensional homology modeling of the CCP modules IV and V and of the B domain was also performed. The complementary information provided by chemical cross-linking and homology modeling studies was used to construct a three-dimensional model of the γ-B monomer, in which module V interacts with the serine protease on the side opposite to both the active site and the Arg446−Ile447 activation site. Also, a tentative three-dimensional model of the (γ-B)2 dimer was built, indicating a loose “head to tail” association of the monomers, with the active sites facing opposite directions toward the outside of the dimer. The latter model is compared with available low-resolution structural data, and its functional implications are discussed in terms of the conformational changes occurring during C1r activation.Keywords
This publication has 24 references indexed in Scilit:
- Ready for a motif submission? A proposed checklistTrends in Biochemical Sciences, 1995
- Analysis of the N‐linked oligosaccharides of human C1s using electrospray ionisation mass spectrometryFEBS Letters, 1995
- Solution Structure of a Pair of Complement Modules by Nuclear Magnetic ResonanceJournal of Molecular Biology, 1993
- Three-dimensional structure of a complement control protein module in solutionJournal of Molecular Biology, 1991
- Neutron scattering study of the (γ-B) catalytic domains of complement proteases Cl̄r and Cl̄sFEBS Letters, 1990
- Crystal structure of bovine β-trypsin at 1.5 Å resolution in a crystal form with low molecular packing densityJournal of Molecular Biology, 1989
- Functional model of subcomponent C1 of human complementJournal of Molecular Biology, 1986
- The atomic structure of crystalline porcine pancreatic elastase at 2.5 Å resolution: Comparisons with the structure of α-chymotrypsinJournal of Molecular Biology, 1978
- The protein data bank: A computer-based archival file for macromolecular structuresJournal of Molecular Biology, 1977
- Structure of crystalline α-chymotrypsinJournal of Molecular Biology, 1972