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9.B.22 The Leukotoxin Secretion Morphogenesis Protein C (MorC) Family

Gram-negative bacteria display either a flat or an irregular outer membrane. The periodontal pathogen Aggregatibacter (Actinobacillus) actinomycetemcomitans has an irregular outer membrane. Gallant et al., 2008 have identified a gene that is associated with the biogenesis of this morphology. The gene is part of a three-gene operon and codes for a 141-kDa protein designated morphogenesis protein C (MorC), which is conserved in several gram-negative bacteria including Haemophilus influenzae and Pasteurella multocida. Insertional inactivation of this gene resulted in the conversion of an irregularly shaped membrane to a flat membrane. Associated with this morphological change were the autoaggregation of the bacteria during planktonic growth and a concomitant increase in the surface hydrophobicity of the bacterium. The absence of MorC also resulted in the loss of the secretion of leukotoxin but not of ltxA transcription. MorC apparently is critical for membrane morphology and leukotoxin secretion in A. actinomycetemcomitans (Gallant et al., 2008).

The presumed transport reaction catalyzed by MorC is:

Leukotoxin (in) → Leukotoxin (out)

References associated with 9.B.22 family:

Deng, M. and R. Misra. (1996). Examination of AsmA and its effect on the assembly of Escherichia coli outer membrane proteins. Mol. Microbiol. 21: 605-612. 8866482
Gallant, C.V., M. Sedic, E.A. Chicoine, T. Ruiz, and K.P. Mintz. (2008). Membrane morphology and leukotoxin secretion are associated with a novel membrane protein of Aggregatibacter actinomycetemcomitans. J. Bacteriol. 190: 5972-5980. 18621903
Heinz, E., J. Selkrig, M.J. Belousoff, and T. Lithgow. (2015). Evolution of the Translocation and Assembly Module (TAM). Genome Biol Evol 7: 1628-1643. 25994932
Prieto, A.I., S.B. Hernández, I. Cota, M.G. Pucciarelli, Y. Orlov, F. Ramos-Morales, F. García-del Portillo, and J. Casadesús. (2009). Roles of the outer membrane protein AsmA of Salmonella enterica in the control of marRAB expression and invasion of epithelial cells. J. Bacteriol. 191: 3615-3622. 19346309
Selkrig, J., K. Mosbahi, C.T. Webb, M.J. Belousoff, A.J. Perry, T.J. Wells, F. Morris, D.L. Leyton, M. Totsika, M.D. Phan, N. Celik, M. Kelly, C. Oates, E.L. Hartland, R.M. Robins-Browne, S.H. Ramarathinam, A.W. Purcell, M.A. Schembri, R.A. Strugnell, I.R. Henderson, D. Walker, and T. Lithgow. (2012). Discovery of an archetypal protein transport system in bacterial outer membranes. Nat Struct Mol Biol 19: 506-10, S1. 22466966