Biologically Active Isoforms of CobB Sirtuin Deacetylase in Salmonella enterica and Erwinia amylovora

Abstract

Sirtuins are NAD؉ -dependent protein deacylases that are conserved in all domains of life and are involved in diverse cellular processes, including control of gene expression and central metabolism. Eukaryotic sirtuins have N-terminal extensions that have been linked to protein multimerization and cellular localization. Here the first evidence of sirtuin isoforms in bacteria is reported. The enterobacterium Salmonella enterica synthesizes two isoforms of CobB sirtuin, a shorter 236-amino-acid isoform (here CobB S ) and a longer 273-amino-acid isoform (here CobB L ). The N-terminal 37-amino-acid extension of CobB L is amphipathic, containing 18 basic amino acids (12 of which are Arg) and 13 hydrophobic ones; both isoforms were active in vivo and in vitro. Northern blot and transcription start site analyses revealed that cobB is primarily expressed as two monocistronic cobB mRNAs from two transcription start sites, one of which was mapped within the neighboring ycfX gene and the other of which was located within cobB. Additionally, a low-abundance ycfX-cobB bicistronic mRNA was observed which could encode up to three proteins (YcfX, CobB L , and CobB S ). CobB L isoforms are common within the family Enterobacteriaceae, but species of the genus Erwinia (including the plant pathogen Erwinia amylovora) encode only the CobB L isoform. The CobB L isoform from E. amylovora restored growth of as S. enterica cobB mutant strain on low acetate.

Acylation of Biomolecules in Prokaryotes: a Widespread Strategy for the Control of Biological Function and Metabolic Stress

“…This results in the production of a long isoform (CobB L ) (273 amino acids [aa]) and a short isoform (CobB S ) (236 aa), which lacks 37 of the amino acids present in CobB L (249). Interestingly, both the CobB L and CobB S isoforms are active, although CobB S is the dominant isoform in vivo and is produced at ϳ10-fold-higher levels (249). The presence of the dual start codons is not limited to S. enterica and is found throughout the enterobacteria.…”

cAMP‐CRP co‐ordinates the expression of the protein acetylation pathway with central metabolism in Escherichia coli

“…Moreover, in S. enterica the cobB gene is expressed from two promoters that are independent of its neighbouring gene ( ycfX , located only 18 bp apart from cobB ), each one located within ycfX and cobB ORFs respectively. It has been proposed that the expression of two CobB isoforms with independent transcription start sites would allow S. enterica to differentially regulate them (Tucker and Escalante‐Semerena, 2010). In B. subtilis , the control of protein deacetylation is more complex as two deacetylases are involved: SrtN, an NAD + ‐dependent protein deacetylase (sirtuin) and AcuC, a deacetylase that does not require NAD + as co‐substrate (Gardner and Escalante‐Semerena, 2008).…”

Two promoters and two translation start sites control the expression of the Shigella flexneri outer membrane protease IcsP

“…Whether our observation is restricted to the genome of S. flexneri 2a strain 301 or is the general property of microbial genomes will require additional studies. It should be noted that recent work by Tucker and Escalante-Semerena (Tucker and Escalante-Semerena 2010), demonstrates that two translation start sites allow the production of two isoforms of CobB to be made from a single gene in Salmonella enterica and that these two isoforms have different biological activities. Our findings, in conjunction with these studies, imply that the use of alternative translation start sites may increase the size of the proteome and, in some instances, lead to a larger range of physiological functions being encoded by the bacterial genome than was previously acknowledged.…”