Previous studies suggest that the number of proteins containing covalently bound biotin is larger than previously thought. Here, we report the identity of some of these proteins. Using mass spectrometry we discovered 108 novel biotinylation sites in the human embryonic kidney HEK293 cell proteome; members of the heat shock protein (HSP) superfamily were overrepresented among the novel biotinylated proteins. About half of the biotinylated proteins also displayed various degrees of methionine oxidation, which is known to play an important role in the defense against reactive oxygen species; for biotinylated HSPs, the percent of methionine sulfoxidation approached 100%. Protein structure analysis suggests that methionine sulfoxides localize in close physical proximity to the biotinylated lysines on the protein surface. Mass spectrometric analysis revealed that between 1 and 5 of the methionine residues in the C-terminal KEEKDPGMGAMGGMGGGMGGGMF motif are oxidized in HSP60. The likelihood of methionine sulfoxidation is higher if one of the adjacent lysine residues is biotinylated. Knockdown of HSP60 caused a 60% increase in the level of reactive oxygen species in fibroblasts cultured in biotin-sufficient medium. When HEK293 cells were transferred from biotin-sufficient medium to biotin-free medium, the level of reactive oxygen species increased by >9 times compared with baseline controls and a time-response relationship was evident. High levels of methionine sulfoxidation coincided with cell cycle arrest in the G0/G1 and S phases in biotin-depleted cells. We conclude that biotinylation of lysines synergizes with sulfoxidation of methionines in heat-shock proteins such as HSP60 in the defense against reactive oxygen species.
Iron homeostasis is tightly regulated, and the peptide hormone hepcidin is considered to be a principal regulator of iron metabolism. Previous studies in a limited number of mouse strains found equivocal sex- and strain-dependent differences in mRNA and serum levels of hepcidin and reported conflicting data on the relationship between hepcidin () mRNA levels and iron status. Our aim was to clarify the relationships between strain, sex, and hepcidin expression by examining multiple tissues and the effects of different dietary conditions in multiple inbred strains. Two studies were done: first, mRNA, liver iron, and plasma diferric transferrin levels were measured in 14 inbred strains on a control diet; and second, mRNA and plasma hepcidin levels in both sexes and iron levels in the heart, kidneys, liver, pancreas, and spleen in males were measured in nine inbred/recombinant inbred strains raised on an iron-sufficient or high-iron diet. Both sex and strain have a significant effect on both hepcidin mRNA (primarily a sex effect) and plasma hepcidin levels (primarily a strain effect). However, liver iron and diferric transferrin levels are not predictors of mRNA levels in mice fed iron-sufficient or high-iron diets, nor are the mRNA and plasma hepcidin levels good predictors of tissue iron levels, at least in males. We also measured plasma erythroferrone, performed RNA-sequencing analysis of liver samples from six inbred strains fed the iron-sufficient, low-iron, or high-iron diets, and explored differences in gene expression between the strains with the highest and lowest hepcidin levels. Both sex and strain have a significant effect on both hepcidin mRNA (primarily a sex effect) and plasma hepcidin levels (primarily a strain effect). Liver iron and diferric transferrin levels are not predictors of mRNA levels in mice, nor are the mRNA and plasma hepcidin levels good predictors of tissue iron levels, at least in males.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.