Procarboxypeptidase A activation segment compared to structures of other proteins.

The 94-residue activation segment of procarboxypeptidase A was compared with segments of other proteins. No significant homologies were observed towards other activation segments, but an inter-domain segment preceding the serine-protease part of complement factor B showed some structural relationships with the N-terminal region of the procarboxypeptidase A activation segment. This may reflect common functional and organizational patterns. In contrast, the present comparisons do not give functional or further sequence support to previously proposed structural homologies with helix-loop-helix (EF-hand) calcium-binding proteins.