Secpathway

Secpathway refers to the conserved protein translocation system responsible for exporting many proteins across cellular membranes. In bacteria, the Sec-dependent pathway moves unfolded polypeptides across the inner membrane into the periplasm or beyond the cell, while in eukaryotes a homologous Sec61-based translocon mediates import into the endoplasmic reticulum. The pathway is essential for a wide range of cellular processes, including secretion of enzymes, toxins, and cell-surface proteins.

A core bacterial Sec pathway comprises SecA, an ATPase that powers translocation, and the SecYEG channel that forms the membrane pore. A cytosolic chaperone SecB helps keep preproteins unfolded, and the SecDF-YajC complex assists translocation and folding. Preproteins are targeted by signal peptides, which direct them to the membrane and can determine whether transit is co-translational or post-translational. After crossing the membrane, many proteins are cleaved by signal peptidases to remove their targeting sequences.

In eukaryotes, the Sec61 complex (Sec61αβγ) forms the core translocon at the endoplasmic reticulum, where nascent polypeptides are targeted by the signal recognition particle pathway. Accessory factors such as Sec62, Sec63, and BiP aid certain post-translational imports, and ER-associated processing includes glycosylation and disulfide-bond formation.

Significance and evolution of the Secpathway reflect its central role in protein sorting and membrane biogenesis. It is a subject of extensive research due to its fundamental biology, its involvement in secretion-related processes, and its potential as a target for antimicrobial strategies.