Outer Membrane Proteins
The outer membrane (OM) of Gram-negative bacteria is in direct contact with the external environment, and contains proteins, lipoproteins, phospholipids, and lipopolysaccharides (LPSs). OM proteins (OMPs) are often directly involved in the virulence of pathogenic bacteria. The Shigella flexneri OMP called IcsA protein is essential for bacterial motility inside infected human cells, while another S. flexneri OMP is IcsP which is a protease that cleaves IcsA.
IcsA and IcsP
The IcsA protein is a large 116 kDa outer membrane protein which is able to interact with actin regulatory proteins within the cytosol of host (human and animal) cells to trigger polymerisation of actin and hence actin-based motility. IcsA is a member of the autotransporter family of proteins, and has an 85 kDa amino terminal passenger (or alpha domain) and a 37 kDa carboxy terminal transporter (or beta domain) that is located in the outer membrane. The IcsA protein is it is targeted to and predominantly localised at the old cell pole in strains that have intact LPS. Polar localisation is relaxed in strains unable to produce either LPS O antigens or the IcsP protease.
Zumsteg, A.B., Goosmann, C., Brinkmann, V., Morona, R., and Arturo Zychlinsky, A. (2014) IcsA is an adhesin in Shigella flexneri that is regulated by the activity of the Type III secretion system. Cell Host and Microbe 15:435-445.
Tran, E.N, Doyle, M.T, and Morona R. (2013) LPS unmasking of Shigella flexneri reveals preferential localisation of tagged outer membrane protease IcsP to septa and new poles. PLoS One. 2013 Jul 25;8(7):e70508. doi: 10.1371/journal.pone.0070508.
Teh, M.Y. and Morona, R. (2013) Identification of Shigella flexneri IcsA residues affecting interaction with N-WASP, and evidence for IcsA-IcsA co-operative interaction. PLoS One. 2013; 8(2):e55152. doi: 10.1371/journal.pone.0055152. Epub 2013 Feb 6.
Teh, M.Y., Tran, E.N., and Morona, R. (2012) Absence of O-antigen suppresses Shigella flexneri IcsA autochaperone region mutations. Microbiology (SGM). 158: 2835-2850.
May, K.L., Grabowicz, M., Polyak, S.W. and Morona, R. (2012) Self-association of the Shigella flexneri IcsA autotransporter. Microbiology (SGM). 158:1874-1883.
Lum, M. and Morona, R. (2012) IcsA autotransporter passenger promotes increased fusion protein expression on the cell surface. Microbial Cell Factories. 11:20. doi: 10.1186/1475-2859-11-20.
May, K.M. and Morona, R. (2008) Mutagenesis of the Shigella flexneri autotransporter IcsA reveals novel functional regions involved in IcsA biogenesis and recruitment of host neural Wiscott-Aldrich syndrome protein. J Bacteriol. 190:4666-4676.