New findings regarding the identification of an arginylated protein of 125 kDa molecular mass.

MARÍA BELÉN DECCA; MAURICIO R. GALIANO; HÉCTOR S. BARRA; MARTA E. HALLAK

Buenos Aires

Congreso; 18th Biennial Meeting of the International Society for Neurochemistry and 32nd annual Meeting of the American Society for Neurochemistry; 2001

ISN-ASN y la Sociedad Argentina de Neuroquimica

One of the post-traslational modifications of proteins consists on the covalent incorporation of arginine into the NH2-terminus. This is one of the mechanism by which proteins to be degraded are recognized by the proteosome. In soluble rat brain extracts between the proteins modified by this reaction, one has been characterized, as the microtubule associated protein denominated N-STOP. The 14C-arginylated protein shows an electrophoretic mobility in SDS-PAGE similar to that of N-STOP protein and it is immunoprecipitated by a monoclonal antibody against N-STOP. Because of these observations, it was assumed that the N-STOP is a substrate of the arginylation reaction. However, in recent experiments we found that: 1) N-STOP from mouse brain, migrates in SDS-PAGE as a protein of 116 kDa whereas the 14C-arginilated protein was at 125 kDa;  2) The N-STOP protein interacts with Ca+2 /calmodulin, but the 125 kDa 14C-arginilated protein does not; 3) By 2D electrophoresis the 125 kDa 14C-arginilated protein was separated from the N-STOP protein. Furthermore in CHOK1 cells overexpressing N STOP, this protein was not arginylated. With this new information we proposed that the 125 kDa protein that is substrate of the arginylation reaction is different from the N-STOP. However is still intriguing the relationship we earlier found between these two proteins. Identification of the 125-kDa protein will be an important step to resolve this question. Supported by: SECyT- UNC, FONCYT- CONICET Ministerio de Salud de la Nación.