Variant Codes (first pass):

1 = Substantial number of components
9 = Misc. components


Hydrogenase nickel incorporation protein HypA -- Zn finger protein that inserts nickel into some [NiFe] hydrogenases
Hydrogenase nickel incorporation protein HybF -- Zn finger protein that inserts nickel into other [NiFe] hydrogenases

Hydrogenase nickel incorporation-associated protein HypB -- a GTPase that is required for insertion of nickel by HypA and HybF

Hydrogenase metallocenter assembly protein HypC -- Fe(CN)2(CO) scaffold and transfer complex component (with HypD)
Hydrogenase metallocenter assembly protein HybG -- Fe(CN)2(CO) scaffold and transfer complex component (with HypD)

Hydrogenase metallocenter assembly protein HypD -- Fe(CN)2(CO) scaffold and transfer complex component (with HypC or HybG)

Hydrogenase metallocenter assembly protein HypE -- carbamoyl-dehydratase -CN synthesis (with HypE?)

Hydrogenase metallocenter assembly protein HypF -- carbamoyl phosphate-dependent transcarbamoylase (to HypE)


Synthesis of the cyanide:

HypE and HypF proteins use cabamoylphosphate to add cyanide to the Fe in the formation of the [NiFe] center.
[Blokesch, M., Paschos, A., Bauer, A., Reissmann, S., Drapal, N., and Bock, A. 2004. Analysis of the
transcarbamoylation-dehydration reaction catalyzed by the hydrogenase maturation proteins HypF and HypE.
Eur. J. Biochem. 271: 3428-36]. Note that there are two moles of cyanide per Fe.


Carbamoylphosphate (= PO4-CONH2)
|
| HypF
|/
| ATP
|/
| (autocatalysis by HypF)
|\
| Pi + PPi
|
HypF-AMP-CONH2
|
| HypE-SH
|/
| (autocatalysis by HypE)
|\
| HypF + AMP
|
HypE-S-CONH2
|
| ATP
|/
| (autocatalysis by HypE)
|\
| H2O + ADP + Pi
|
HypE-S-CN


Formation of Fe-HypCD complex (HypCD complex does not form without iron):

HypC + HypD
|
| Fe
|/
| (autocatalysis by HypCD)
|
Fe-HypCD


Transfer of the cyanide to iron (source and timing of CO addition seems to be unknown):

Fe-HypCD
|
| 2 HypE-S-CN
|/
| (autocatalysis by HypE?)
|\
| 2 HypE-SH
|
Fe(CN)2-HypCD

or

Fe(CO)-HypCD
|
| 2 HypE-S-CN
|/
| (autocatalysis by HypE?)
|\
| 2 HypE-SH
|
Fe(CN)2(CO)-HypCD


Dissociation of HypD might occur later (after interaction with hydrogenase large subunit):

Fe(CN)2(CO)-HypCD
|
|\
| HypD
|
Fe(CN)2(CO)-HypC


Metal insertion into the large subunit apoprotein:

The order appears to be iron then nickel. HypA is the Ni-binding protein. HypB is the GTPase.
HypC might remain bound until the nickel is added.

Paralogs of HypA (n.b., HybF ) and HypC (n.b., HybG) can be specific for different hydrogenases.


hydrogenase large subunit apoprotein
|
| Fe(CN)2(CO)-HypC
|/
| (autocatalysis by HypC)
|\
| HypC
|
Fe(CN)2(CO)-hydrogenase large subunit
|
| Ni + GTP
|/
| HypAB
|\
| GDP + Pi
|
NiFe(CN)2(CO)-hydrogenase large subunit