Protein Export

There are three main systems for protein export.

1. Sec pathway using SecA, D, E, Y C F proteins

SPaseI and II cleave peptides off for export. Sec11a and sec11b have been found in halophiles.

YidC Oxa 1p

2. Tat pathway using TatA, TatCo, TatCt, TatAo TatAt, TatB, TorD and TorA are chaperones that bind to signal sequences bound for Tat protein export.

Tat proteins use protein domain of SRRXFLK can we find this? They transport fully folded proteins. Many halophiles have a lot of K+ in cytoplasm to counter balance extracellular salt. Their proteins have many negative amino acids that help keep the proteins and bacteria from “salting out” and may lead to rapid protein folding. Therefore, the Tet system may be more important than the Sec system.

3. lipobox pathway for lipid-modified proteins, lipobox = [I/L/G/A][A/G/S]"cut_here"C is the target for SPaseII enzymes.

Type I – V secretion systems possible. I is ABC protein transporter

Flagella and pilus or pili proteins. PibD trims off cytoplasmic parts of flagellar proteins