Alpha + Beta Class

II. Alpha-helices on both sides of a beta-sheet

The Flavodoxin fold is a distinct structural motif consisting of a four-stranded beta sheet and four flanking alpha-ehelices. It has been identified in the three-dimensional structures of many proteins. There is, however, little sequence identity between domains with this fold. Note the placement of the helices with respect to the central beta sheet.
e

Carboxypeptidase A. A protease secreted by the pancreas.

The framework of this molecule is a mixed beta sheet consisting of eight strands. How many beta strands are antiparallel to each other?

Six out of eight alpha-helices are packed against the central beta sheet. The zinc atom (magenta sphere) plays an essential role in the mechanism of carboxypeptidase-catalyzed reactions.