523 - Carboxyl-terminal processing may be essential for production of active NiFe hydrogenase in Azotobacter vinelandii

Based on amino acid prediction from gene sequence, the HoxG alpha subunit of the uptake hydrogenase should be about 66.6 kDa, but in the wild-type it appears smaller. In some mutants with accessory genes knocked out, the size matches this number. So this study tried to figure out if post-translational processing was involved in producing active enzyme. N-terminal modification was already ruled out, as that sequence matches the prediction.

What They Saw
They grew Azotobacter vinelandii CA and purified its hydrogenase, then studied its subunits with mass spectrometry.

They observed that the actual size of the larger subunit was 64.9 kDa, smaller than the 66.6 predicted size. The N-terminal was still the same as predicted, so they concluded that about 15 amino acids had been removed from the C-terminal of the subunit. This appears to be necessary for it to function.

Reference:

Gollin, D. J., Mortenson, L. E. & Robson, R. L. Carboxyl-terminal processing may be essential for production of active NiFe hydrogenase in Azotobacter vinelandii. FEBS Letters 309, 371–375 (1992).