Final answer:
The two types of β sheets in protein secondary structure are parallel and antiparallel, which are characterized by the orientation of the N-terminals of adjacent polypeptide chains and linked through hydrogen bonds.
Step-by-step explanation:
The two types of β sheets in protein secondary structure are parallel and antiparallel. The β-pleated sheet conformation is a secondary structure where two or more extended polypeptide chains (or regions within a single chain) are aligned side by side. These chains are connected by hydrogen bonds and can either have their N-terminals facing the same direction which makes them parallel, or facing opposite directions which makes them antiparallel.
The role of the β-pleated sheet is significant in structural proteins, such as silk fibroin, and is also observed in various enzymes. This conformation provides stability and rigidity to the protein structure due to the extensive hydrogen bonding.