Catalytic and thermodynamic properties of tetrahydromethanopterin-dependent serine hydroxymethyltransferase from Methanococcus jannaschii.
The reaction catalyzed by serine hydroxymethyltransferase (SHMT), the transfer of Cbeta of serine to tetrahydropteroylglutamate, represents in Eucarya and Eubacteria a major source of one-carbon (C1) units for several essential biosynthetic processes. In many Archaea, C1 units are carried by modified pterin-containing compounds, which, although structurally related to tetrahydropteroylglutamate, play a distinct functional role. Tetrahydromethanopterin, and a few variants of this compound, are the modified folates of methanogenic and sulfate-reducing Archaea. Little information on SHMT from Archaea is available, and the metabolic role of the enzyme in these organisms is not clear. This contribution reports on the purification and characterization of recombinant SHMT from the hyperthermophilic methanogen Methanococcus jannaschii. The enzyme was characterized with respect to its catalytic, spectroscopic, and thermodynamic properties. Tetrahydromethanopterin was found to be the preferential pteridine substrate. Tetrahydropteroylglutamate could also take part in the hydroxymethyltransferase reaction, although with a much lower efficiency. The catalytic features of the enzyme with substrate analogues and in the absence of a pteridine substrate were also very similar to those of SHMT isolated from Eucarya or Eubacteria. On the other hand, the M. jannaschii enzyme showed increased thermoactivity and resistance to denaturating agents with respect to the enzyme purified from mesophilic sources. The results reported suggest that the active site structure and the mechanism of SHMT are conserved in the enzyme from M. jannaschii, which appear to differ only in its ability to bind and use a modified folate as substrate and increased thermal stability.
Angelaccio
Sebastiana
S
Dipartimento di Scienze Biochimiche A. Rossi Fanelli, Università degli Studi di Roma La Sapienza, Piazzale Aldo Moro 5, Rome 00185, Italy.
Chiaraluce
Roberta
R
Consalvi
Valerio
V
Buchenau
Bärbel
B
Giangiacomo
Laura
L
Bossa
Francesco
F
Contestabile
Roberto
R
D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D004795:Enzyme Stability; D012696:Glycine Hydroxymethyltransferase / Q000737:chemistry* / Q000378:metabolism*; D017017:Methanococcus / Q000201:enzymology*; D011489:Protein Denaturation; D011622:Pterins / Q000378:metabolism*; D011994:Recombinant Proteins; D016415:Sequence Alignment; D013057:Spectrum Analysis; D013379:Substrate Specificity; D013816:Thermodynamics
D011622:Pterins; D011994:Recombinant Proteins; C042416:5,6,7,8-tetrahydromethanopterin; D012696:Glycine Hydroxymethyltransferase