Editing Secretion (section)

==={{anchor|T1SS}}Type I secretion system (T1SS or TOSS)===
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Type I secretion is a chaperone dependent secretion system employing the Hly and Tol gene clusters. The process begins as a leader sequence on the protein to be secreted is recognized by HlyA and binds HlyB on the membrane. This signal sequence is extremely specific for the ABC transporter. The HlyAB complex stimulates HlyD which begins to uncoil and reaches the outer membrane where TolC recognizes a terminal molecule or signal on HlyD. HlyD recruits TolC to the inner membrane and HlyA is excreted outside of the outer membrane via a long-tunnel protein channel.

Type I secretion system transports various molecules, from ions, drugs, to proteins of various sizes (20 – 900 kDa). The molecules secreted vary in size from the small ''[[Escherichia coli]]'' peptide colicin V, (10 kDa) to the ''[[Pseudomonas fluorescens]]'' cell adhesion protein LapA of 520 kDa.<ref>{{cite journal | vauthors = Boyd CD, Smith TJ, El-Kirat-Chatel S, Newell PD, Dufrêne YF, O'Toole GA | title = Structural features of the Pseudomonas fluorescens biofilm adhesin LapA required for LapG-dependent cleavage, biofilm formation, and cell surface localization | journal = Journal of Bacteriology | volume = 196 | issue = 15 | pages = 2775–88 | date = August 2014 | pmid = 24837291 | pmc = 4135675 | doi = 10.1128/JB.01629-14 }}</ref> The best characterized are the [[RTX toxin]]s and the lipases. Type I secretion is also involved in export of non-proteinaceous substrates like cyclic β-glucans and polysaccharides.

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