The three-dimensional structure of the pFc′ fragment of guinea pig IgGl, a dimer of CH3 homology sub-units, has been determined to 3.125 Å nominal resolution by crystallographic analysis. The crystal structure was solved by molecular replacement methods using as a probe the refined structure of a human IgG1 CH1 homology sub-unit. The path of the polypeptide chain has been traced from Gly341 to Ile441. No continuous electron density was found for the N-terminal segment before Gly341. The majority of the amino acid side chains were located in the electron density map. The overall tertiary structure and many features of secondary structure found in other constant region homology sub-units of immunoglobulins are preserved in pFc′. The high homology in amino acid sequence among CH3 regions of different immunoglobulins can be partly explained on the basis of the three-dimensional structure; residues which are involved in contacts essential to the tertiary and quaternary structure of the molecule are conserved or conservatively replaced. Amino acid sequence differences in the CH3 regions of different sub-classes of IgG are analyzed with respect to their position in the three-dimensional structure and the effector function properties of the different sub-classes.
ASJC Scopus subject areas
- Molecular Biology