BBMB Research Seminars

October 11, 2007
Tom Bobik
Department of BBMB
Iowa State University

B12 metabolism in salmonella"

1414 Molecular Biology Buidling
4:10 p.m.

Abstract:

Vitamin B12 is a precursor to methyl-B12 and adenosyl-B12 which are important coenzymes in biology and essential for human health.  To obtain a better general understanding of B12 metabolism, we have been investigating B12-dependent 1,2-propanediol degradation in Salmonella. These studies have provided new insights in B12 processes and unexpectedly uncovered a new type of bacterial microcompartment. Bacterial microcompartments are primitive organelles composed completely of protein subunits. Genomic analyses indicate they are widespread among bacteria and have diverse metabolic functions. Our studies have focused on the microcompartments involved in B12-dependent 1,2-propanediol degradation by Salmonella. These structures have a protein shell that may contain as many as seven different polypeptides and in the lumen are catabolic enzymes needed for 1,2-propanediol degradation as well as enzymes needed to maintain the activity of B12-dependent diol dehydratase which catalyzes the first step of the catabolic pathway. We propose that these microcompartments function to sequester a toxic metabolic intermediate (propionaldehyde), and that the protein shell of microcompartments contains pores that control metabolite entry and exit. We also propose that the general function of bacterial microcompartments is to retain nonpolar metabolites that are poorly retained by lipid bilayers.