With surprising frequency, unexpected ligands identified
in the crystal structure have also indicated the
function of structural genomics proteins. Clues about
the molecular mechanism of the proteins MTH150 and
MTH152 (from M. thermoautotrophicum), HI0139
(from Haemophilus influenzae), and MJ0577 (from
M. jannaschii) were shown by their co-crystallization
with NAD+, FMN (flavin mononucleotide), a selenium
version of S-adenosyl-L-homocysteine, and ATP, respectively31,92,93.
In each case, binding was sufficiently strong
that the protein apparently scavenged the cofactor from
the original expression system. In further tests, MJ0577
was found to hydrolyse ATP to ADP only in the presence
of extract from its source organism, M. jannaschii, indicating
that it might be a molecular switch93.