The monomeric structure of HydA was demonstrated on
an SDS-polyacrylamide gel electrophoresis (SDS-PAGE)
after Coomassie blue staining (Fig. 3A). The N-terminal amino acid sequence of the mature protein was determined
by Edman degradation, which matched the amino acid
sequence deduced from the cDNA sequence (AGPTSECDCPPTPQAKLPHW).
The first 21 amino acids are missing
in the native protein and probably function as a transit
peptide since this sequence terminates with a characteristic
stroma peptidase cleavage site (Val, Arg, Ala) [19]. The
predicted polypeptide derived from the complete open reading
frame of the hydA cDNA has a length of 436 amino
acids with a calculated molecular mass of 47.3 kDa. The
calculated weight of the polypeptide without the transit
peptide region is 45 kDa, which corresponds to the molecular
mass of the purified native protein (Fig. 3B). The
truncated coding region of the hydA cDNA lacking the
transit peptide sequence was amplified by RT-PCR, cloned
into the NdeI/BamHI sites of pET9a and expressed in E. coli
strain BL21 (DE3) pLysS. Antibodies raised against HydA
from C. reinhardtii cross-reacted with the recombinant
HydA protein as well as with the isolated hydrogenase from
C. fusca (Fig. 3B). The heterologous hydrogenase enzyme
was not active, probably because E. coli cannot assemble
the unique active site of the [Fe]-hydrogenase [9].