Tagging via substrate

Onono, F.K., et al. (2010). A tagging-via-substrate approach to detect the farnesylated proteome using Two-dimensional electrophoresis coupled with western blotting. Mol Cell Proteom 9 742-751. 

Kho Y, Kim SC, Jiang C, Barma D, Kwon SW, Cheng JK, Jaunbergs J, Weinbaum C, Tamanoi E, Ealck J, Zhao YM. A tagging-via-substrate technology for detection and pro-teomics of famesylated proteins. Proc. Natl. Acad. Sci. U.S.A. 2004 101 12479-12484. 

Sprung, R., Nandi, A., Chen, Y, Kim, S. C., Barma, D., Falck, J. R., and Zhao, Y. M., Tagging-via-substrate strategy for probing O-GlcNAc modified proteins. Journal of Proteome Research, 4, 950-957, 2005. 

Given the ability of ACBP3s to bind PC (the phospholipid substrate of FADX), does ACBP3A help to channel eleostearate out of PC and into TAG via a traditional acyl-CoA binding role, or a PC-binding role These questions await future research. 

It has been reported that the GRR that spans amino acid residues 476-304 in human pl05, is an important structural motif required for the generation of the p50 subunit of NF-kB (10). However, the mechanisms involved in this unique reaction have remained enigmatic. Since degradation of a protein via the ubiquitin pathway involves two steps, conjugation of ubiquitin and proteasomal degradation of the tagged substrate, it was important first to identify the step affected by the GRR. 

The first evidence for the existence of the methylation of a prenylated peptidyl substrate was found in two jelly fungi, Tremella mesenterica and Tremella brasiliensis [30,31]. These peptide sequences are similar to the a-mating factor found in Saccharomyces cerevisiae, which is also prenylated at the C-terminus and contains an a-carboxyl methyl ester [32]. The gene product of the STEM in S. cerevisiae was found to be responsible for the methylation event for the a-factor-mating pheromone and the enzymatic activity of this methyltransferase was found only in the cellular membrane fractions [33,34]. Further analyses of Stel4p via epitope tagging determined that the enzyme is localized to the ER membrane and possesses six transmembrane segments, with majority of the enzyme exposed to the cytosol [35,36]. 

Human pancreatic lipase (HPL) alone is inactive in vitro on an emulsified TAG substrate in the presence of supramiceUar concentrations of bile salts such as those found in the small intestine. Bile salts are amphiphilic molecules that bind to the oil-water interface and prevent pancreatic hpase adsorption, and thus hpo-lysis, from occurring [3, 4]. The inhibition by bile salts can, however, be reversed by the specific pancreatic hpase cofactor cohpase [3, 5-7], via the formation of a specific 1 1 hpase-cohpase complex. 

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