P'stutzeri CynD is a 14 subunit homooligomeric spiral

1
P.stutzeri CynD is a 14 subunit homo-oligomeric
spiral
pH 8
pH 6
B. pumilis CynD apparently has 16 subunits but
we will return to this later
2
The Effect of Surface Mutations on Activity
3
Relationship of solved structures to the
bacterial and plant nitrilases, CynD, and fungal
cyanide hydratrases
Plant nitrilases
Solved structures
CynD
Bacterial nitrilases
Fungal cyanide hydratases
4
Sequence Alignment
The location of the active site
Insertions relative to the crystal homologues
5
Sequence Alignment
The components of the A surface
6
Structural transition in B. pumilus nitrilase

• The transitions between pH 6 and pH 5.4 may
  involve the titration of a histidine.
• At pH 5.4 the nitrilase is a regular helix having
  9.4 subunits per turn ( for dimer model ?f
  -76.7, ?z1.58 nm )

pH 6
pH 8
Helical reconstructions were made with IHRSR
according to Egelman
pH 5.4
7
D surface
SPHVQRLLDAARDHN SLAIQKISEAAKRNE SEAVQKISAAARKNK SS
EMRRIRAAARDNQ
R. rhodochrous J1
B. pumilus
P. stutzeri
G. sorghi
Potential for two pairs of salt bridges in B.
pumilus, R. rhodochrous and G. sorghi Repulsion
in P. stutzeri - no long fibres
P. stutzeri
B. pumilus
8
Is it possible to explain the transition from
spirals to helices which occurs in B. pumilus
CynD at pH 5.4?
The pH 6 structure is possibly a hybrid between
a terminating 14mer and a terminating 18mer
E
90o
pH 6.0
pH 5.4
Recall that the histidines are located in the
C-terminal extension on the inside of the spiral
Hypothesis The charged histidines repel one
another disrupting the E surface interaction and
create space for an additional dimer which is
located by the D surface interactions.