Quarternary Protein Structure
The
structure shown has two subunits, each comprising three
alpha helices and
three beta sheets.
Note that the subunits are held together by ionic
bonds between two beta sheets running in opposite N-C
direction. [The two subunits are said to show a dyad axis
of symmetry].
Figure © 2012 TA Brown, Introduction
to Genetics (1st ed.); additional
text © 2014 by Steven M. Carr