FMN is covalently attached to a threonine residue in the NqrB and NqrC subunits of Na(+)-translocating NADH-quinone reductase from Vibrio alginolyticus.
The Na(+)-translocating NADH-quinone reductase (NQR) from Vibrio alginolyticus is composed of six subunits (NqrA to NqrF). We previously demonstrated that both NqrB and NqrC subunits contain a flavin cofactor covalently attached to a threonine residue. Fluorescent peptide fragments derived from the NqrB and NqrC subunits were applied to a matrix-assisted laser desorption ionization time-of-flight mass spectrometer, and covalently attached flavin was identified as FMN in both subunits. From post-source decay fragmentation analysis, it was concluded that FMN is attached by a phosphate group to Thr-235 in the NqrB subunit and to Thr-223 in the NqrC subunit. The phosphoester binding of FMN to a threonine residue reported here is a new type of flavin attachment to a polypeptide.
Hayashi
M
M
Laboratory of Membrane Biochemistry, Faculty of Pharmaceutical Sciences, Chiba University, Chiba, Japan. makiha@p.chiba-u.ac.jp
Nakayama
Y
Y
Yasui
M
M
Maeda
M
M
Furuishi
K
K
Unemoto
T
T
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D005486:Flavin Mononucleotide / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D021122:Protein Subunits; D011808:Quinone Reductases / Q000737:chemistry* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013912:Threonine / Q000378:metabolism*; D014733:Vibrio / Q000201:enzymology*
D001426:Bacterial Proteins; D010710:Phosphates; D021122:Protein Subunits; D013912:Threonine; D005486:Flavin Mononucleotide; C084142:sodium-translocating NADH-quinone reductase; D011808:Quinone Reductases