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Figure 4.
Fig. 4. Effect of the two mutations on the RCL insertion
mechanism. A: During the preinsertion (β-strand s3A in blue
moved to the position in green) and the full insertion of the
RCL (β-strand s3A in orange) Val188 has to slide into groove 1
of α-helix hB (residues 53–56). Likewise, Asn186 has to slide
into groove 2 of α-helix hB (residues 56–60). B: Effect of
the Ser53Pro mutation. β-Strand s6A and α-helix hB of the
cleaved form are colored in orange. By adding a new hydrophobic
residue in the native form (in dark blue) and in the preinserted
form (in green), Val188 of β-strand s3A can make a hydrophobic
interaction with Pro53. After RCL insertion, a rearrangement in
the bottom part of β-strand s3A occurs, affecting the position
of Val188. Since this hydrophobic interaction must be disrupted
after preinsertion to fully insert the RCL, the rate of
insertion could be reduced. C: Effect of the Ser56Arg mutation.
Arg56 replaces Ser56, which normally swings during the insertion
of the reactive loop [28]. Conversely, in the native form and in
the preinserted form (here in green) the Nε side chain of Arg56
can hydrogen-bond the Oδ side chain of Asn186. The Nη1 or Nη2
side chain of Arg56 will also hydrogen-bond the Oδ side chain
of Asn94. Arg56 is at the place where Asn186 has to slide when
the loop is fully inserted. To fully insert the RCL, Arg56 must
lose its hydrogen bonds and shift into another position, that is
also slowing down the rate of the full insertion. Prepared with
Setor [31].
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