Pyridoxal 5′-phosphate (the active form of vitamin B
6
) is a cofactor that is important for a broad number of biochemical reactions and is essential for all forms of life. Organisms that can synthesize pyridoxal 5′-phosphate use either the deoxyxylulose phosphate-dependent or -independent pathway, the latter is encoded by a two-component pyridoxal 5′-phosphate synthase.
Saccharomyces cerevisiae
contains three paralogs of the two-component
SNZ/SNO
pyridoxal 5′-phosphate synthase. Past work identified the biochemical activity of
Snz1p
,
Sno1p
and provided
in vivo
data that
SNZ1
was involved in pyridoxal 5′-phosphate biosynthesis.
Snz2p
and
Snz3p
were considered redundant isozymes and no growth condition requiring their activity was reported. Genetic data herein showed that either
SNZ2
or
SNZ3
are required for efficient thiamine biosynthesis in
Saccharomyces cerevisiae
. Further,
SNZ2
or
SNZ3
alone could satisfy the cellular requirement for pyridoxal 5′-phosphate (and thiamine), while
SNZ1
was sufficient for pyridoxal 5′-phosphate synthesis only if thiamine was provided. qRT-PCR analysis determined that
SNZ2
,
3
are repressed ten-fold by the presence thiamine. In total, the data were consistent with a requirement for PLP in thiamine synthesis, perhaps in the
Thi5p
enzyme, that could only be satisfied by
SNZ2
or
SNZ3
. Additional data showed that
Snz3p
is a pyridoxal 5′-phosphate synthase
in vitro
and is sufficient to satisfy the pyridoxal 5′-phosphate requirement in
Salmonella enterica
when the medium has excess ammonia.