Secondary structure of a complement control protein module by two-dimensional 1H NMR

Area of Science:

• Biochemistry
• Structural Biology
• Immunology

Background:

• The complement control protein (CCP) module, also known as the short consensus repeat, is a conserved domain found in numerous extracellular proteins, including key components of the complement cascade.
• Over 140 CCP modules are present in more than 20 different mosaic proteins, highlighting their functional significance.
• Understanding the structure of individual CCP modules is essential for elucidating the function of these complex proteins.

Purpose of the Study:

• To determine the solution structure of an isolated CCP module.
• To compare the experimentally determined secondary structure with existing predictions.
• To identify conserved residues involved in stabilizing the CCP module's fold.

Main Methods:

• Expression of the 16th CCP module from human complement factor H in a yeast vector.
• Analysis of two-dimensional 600-MHz 1H NMR spectra recorded at pH 3.3 and 6.0.
• Determination of secondary structure elements, including extended segments, beta-sheets, and turns.

Main Results:

• The isolated CCP module folds with a similar disulfide bond pattern to the native protein.
• The secondary structure consists of extended segments, double-stranded antiparallel beta-sheets, and a triple-stranded beta-sheet.
• Experimentally determined secondary structure shows overall resemblance to predictions but differs in turn details.
• Conserved amino acid residues appear critical for stabilizing the overall fold.

Conclusions:

• The study provides the first detailed solution structure of an isolated CCP module.
• The findings validate computational predictions while highlighting discrepancies in specific structural features like turns.
• Conserved residues play a significant role in maintaining the structural integrity of CCP modules.