Active site structure of methylamine dehydrogenase: hydrazines identify C6 as the reactive site of the tryptophan-derived quinone cofactor.
To identify the reactive part of the orthoquinone function of the tryptophan-derived cofactor found in methylamine dehydrogenase (MADH), we have determined the crystal structures of MADH from Thiobacillus versutus inhibited by methylhydrazine and (2,2,2-trifluoroethyl)hydrazine. Extra electron density attached to C6 of the tryptophyl tryptophanquinone cofactor shows that this atom and not C7 is the reactive part of the ortho-quinone moiety. The density retained after hydrazine inhibition is much less extensive than expected, however, suggesting that partial breakdown of the inhibitors after reaction with the cofactor may take place. A detailed description is presented of the cofactor environment in an improved model of MADH which now includes information from the recently determined gene sequence of the cofactor-containing subunit [Ubbink, M., van Kleef, M.A.G., Kleinjan, D., Hoitink, C.W.G., Huitema, F., Beintema, J.J., Duine, J.A., & Canters, G.W. (1991) Eur. J. Biochem. 202, 1003-1012]. We hypothesize that Asp76 is responsible for proton abstraction from the alpha-carbon of the substrate during catalysis.
Huizinga
E G
EG
Department of Chemistry, Groningen University, The Netherlands.
van Zanten
B A
BA
Duine
J A
JA
Jongejan
J A
JA
Huitema
F
F
Wilson
K S
KS
Hol
W G
WG
D000595:Amino Acid Sequence; D001665:Binding Sites; D006834:Hydrazines / Q000494:pharmacology*; D045563:Indolequinones; D008969:Molecular Sequence Data; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D011809:Quinones / Q000378:metabolism*; D013855:Thiobacillus / Q000201:enzymology; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000378:metabolism
D006834:Hydrazines; D045563:Indolequinones; D011809:Quinones; C070569:tryptophan tryptophylquinone; D014364:Tryptophan; C021567:methylamine dehydrogenase; D000587:Oxidoreductases Acting on CH-NH Group Donors