(Speaker Term: 7/1/13 - 6/30/15)
Department of Microbiology
The Ohio State University
484 West 12th Avenue
Columbus, OH 43210-1292
Speaker’s URL: http://microbiology.osu.edu/faculty/krzycki-joseph
LECTURE TOPICS AND DESCRIPTIONS
The Biosynthesis and Genetic Encoding of Pyrrolysine, an Amino Acid Essential for Methanogenesis from Methylamines
The study of methanogenic Archaea has led to the discovery of many unusual enzymes, cofactors, and metabolites. Of these, a novel genetically encoded amino acid was perhaps the most unusual. Methanogens can utilize various methylamines as methane sources. Elucidation of these pathways led to the description of the methyltransferases that initiate methanogensis from different methylamines. Each type of methylamine methyltransferase gene contains an in-frame amber stop codon which is decoded as pyrrolysine. Pyrrolysine can be added to the genetic code of a naïve organism upon transformation with the five pyl gene. The pyl gene products function in the biosynthesis and the genetic encoding of pyrrolysine. Entrance to the genetic code is granted by the pylS and pylT genes. PylS is an aminoacyl-tRNA synthetase specific for pyrrolysine that charges the amber decoding tRNAPyl, encoded by pylT. The remaining Pyl proteins are capable of synthesizing the ring and acyl chain of pyrrolysine from two lysines. PylB is a novel Radical SAM lysine mutase, which provides the precursor that will form the distinctive pyrroline ring of pyrrolysine by rearranging the skeleton of lysine, which is joined by PylC to another lysine before dehydrogenation by PylD results in pyrrolysine, which is co-translationally inserted into the growing methylamine methyltransferase. Upon deletion of pylT, methanogenesis from methylamine is no longer carried out by methanogens.
The Function and Family Relationships of Pyrrolysine, a “One Carbon” Amino Acid
Pyrrolysine is the 22nd genetically encoded amino acid to be discovered. It is found in three non-homologous families of methylamine methyltransferases, and these enzymes present the major rationale for why pyrrolysine has joined the small group of genetically encoded amino acids. The proposed function of pyrrolysine is to provide a means to activate methylamines for transfer to corrinoid proteins in the initial reactions of methanogenesis. Pyrrolysine’s role as a catalytic amino acid necessary for methyl transfer is supported by both genetic and biochemical data, as well as the structures of two families of methylamine methyltransferases. We gained new insight into the function and evolutionary history of pyrrolysine by examining homologs of methylamine methyltransferases that naturally lack pyrrolysine, and which are encoded in a large number of genomes. We recently described the enzymatic activity of one such “non-Pyl” protein family. The novel function of this protein family provides understanding of how evolution to include pyrrolysine would impart new functionality to an already existing family of methyltransferases.
BIOGRAPHICAL SKETCH – Joseph Adrian Krzycki
As an NSF pre-doctoral fellow, Krzycki did seminal work on the major route found in nature for methane formation by microbes called methanogens. As a postdoc, he identified a methanogen DNA binding protein that was later found to be related to histone proteins that organize human genes. As a professor, he focused on understanding routes for methane formation from abundant methylated compounds found in natural environments. His lab has identified the proteins and genes essential for methane formation from five such substrates. They found some genes were interrupted by apparent “stop” signals, an observation which led to discovery of the 22nd genetically encoded amino acid, pyrrolysine. Pyrrolysine was recognized by Discover magazine as among the top discoveries of 2002. The Krzycki lab showed that methanogenesis from nitrogenous compounds required genetic code expansion to include pyrrolysine, and that this was mediated by as few as five genes. These five genes can reprogram the genetic code of E. coli to include pyrrolysine. Recently, the Krzycki lab described the complete route of pyrrolysine biosynthesis from the simpler amino acid, lysine. Dr. Krzycki has been named a Distinguished Scholar of the Ohio State University and is a member of the American Academy of Microbiology. He recently delivered the Division K Lecture at the 2012 Annual Meeting of the American Society for Microbiology.
CV is available upon request from firstname.lastname@example.org at ASM Headquarters.
ASM MEMBERSHIP AFFILIATION – Joseph Adrian Krzycki
Primary Division: K (Microbial Physiology & Metabolism)
Secondary Division: I (General Microbiology)