On p 42 of the text, Oligomerization by beta sheet formation, it is noted that the proteins Raf and Rap come together to form a heterodimer, by joining the into one continuous beta sheet. The in a classic sheet orientation.
In addition to the H-bonding between the two strands, there is also substantial , much of it .
There is also at least one .
Different views of the backbone:
But thinking a little harder, would the H-bonds between strands be sufficient to drive dimerization? Let's look at as well.