Diversity of Protein and mRNA Forms of Mammalian Methionine Sulfoxide Reductase B1 Due to Intronization and Protein Processing

Authors

Xinwen Liang, University of Nebraska-Lincoln
Dmitri E. Fomenko, University of Nebraska-LincolnFollow
Deame Hua, University of Nebraska-Lincoln
Alaattin Kaya, University of Nebraska-Lincoln
Vadim N. Gladyshev, Harvard Medical SchoolFollow

Date of this Version

2010

Citation

Liang X, Fomenko DE, Hua D, Kaya A, Gladyshev VN (2010) Diversity of Protein and mRNA Forms of Mammalian Methionine Sulfoxide Reductase B1 Due to Intronization and Protein Processing. PLoS ONE 5(7): e11497. doi:10.1371/journal.pone.0011497

Comments

Copyright 2010 Liang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License.

Abstract

Background: Methionine sulfoxide reductases (Msrs) are repair enzymes that protect proteins from oxidative stress by catalyzing stereospecific reduction of oxidized methionine residues. MsrB1 is a selenocysteine-containing cytosolic/nuclear Msr with high expression in liver and kidney.

Principal Findings: Here, we identified differences in MsrB1 gene structure among mammals. Human MsrB1 gene consists of four, whereas the corresponding mouse gene of five exons, due to occurrence of an additional intron that flanks the stop signal and covers a large part of the 39-UTR. This intron evolved in a subset of rodents through intronization of exonic sequences, whereas the human gene structure represents the ancestral form. In mice, both splice forms were detected in liver, kidney, brain and heart with the five-exon form being the major form. We found that both mRNA forms were translated and supported efficient selenocysteine insertion into MsrB1. In addition, MsrB1 occurs in two protein forms that migrate as 14 and 5 kDa proteins. We found that each mRNA splice form generated both protein forms. The abundance of the 5 kDa form was not influenced by protease inhibitors, replacement of selenocysteine in the active site or mutation of amino acids in the cleavage site. However, mutation of cysteines that coordinate a structural zinc decreased the levels of 5 and 14 kDa forms, suggesting importance of protein structure for biosynthesis and/stability of these forms.

Conclusions: This study characterized unexpected diversity of protein and mRNA forms of mammalian selenoprotein MsrB1.