Final answer:
Combinations of signal anchor and TM helices in the synthesis of integral proteins lead to topological diversity of multi-pass TM proteins due to the presence of multiple stop-transfer sequences and hydrophobic alpha-helical domains.
Step-by-step explanation:
Combinations of signal anchor and TM (transmembrane) helices cause topological diversity of multi-pass TM proteins. This diversity is due to the multiple stop-transfer sequences within the polypeptide chain that allow the protein to span the membrane multiple times. These alpha-helical domains are hydrophobic and trap the protein within the fatty acid interior of the membrane, contributing to its final topology.
During the synthesis and insertion of transmembrane proteins into the membrane, the orientation of the N- and C-termini is determined by how many times the protein crosses the membrane. Moreover, as proteins move through the endomembrane system, from the RER to the Golgi apparatus, they are sorted and directed to their final destinations. The sorting relies in part on the topological arrangement of transmembrane proteins, which is influenced by the anchoring helices and sequences dictating the transmembrane passages.