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Related Experiment Videos

Crystal structure of a complement factor D mutant expressing enhanced catalytic activity

S Kim1, S V Narayana, J E Volanakis

  • 1Department of Medicine, University of Alabama at Birmingham 35294-0006, USA.

The Journal of Biological Chemistry
|October 13, 1995
PubMed
Summary

Complement factor D, a protease, exhibits low reactivity due to its unique structure. Mutating specific residues to mimic trypsin significantly increased its catalytic activity, explaining its resting-state behavior.

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Area of Science:

  • Biochemistry
  • Enzymology
  • Complement System

Background:

  • Complement factor D is a serine protease with a unique regulation mechanism.
  • Its activity relies on conformational changes induced by its substrate, C3bB, rather than zymogen cleavage.
  • Factor D possesses atypical conformations in its catalytic center and substrate binding site.

Purpose of the Study:

  • To investigate the structural basis for the low catalytic activity of complement factor D in its resting state.
  • To explore the role of specific residues in factor D's atypical conformation and reactivity.

Main Methods:

  • Site-directed mutagenesis was used to replace serine residues 94, 214, and 215 in factor D with corresponding trypsin residues (tyrosine, serine, and tryptophan).
  • Comparative analysis of catalytic activity between wild-type and mutant factor D.

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Main Results:

  • Mutating Ser94, Thr214, and Ser215 to Tyr, Ser, and Trp, respectively, resulted in significantly increased catalytic activity.
  • The mutations induced a more typical serine protease alignment of the catalytic triad (His57, Asp102, Ser195).
  • These findings offer a partial structural explanation for the low reactivity of resting-state factor D.

Conclusions:

  • The atypical conformation of complement factor D's catalytic residues contributes to its low basal activity.
  • Mimicking trypsin's residue configuration partially restores and enhances factor D's catalytic function.
  • Structural insights into factor D's regulation can inform the development of complement system modulators.