Biomedical Engineering Reference
In-Depth Information
Figure 7.2
Zinc coordination in the active site of PfA-M1. Carbon atoms of residues
are colored green, zinc ion is shown as a black sphere, and the water
molecule is shown as a light-yellow sphere. Metallo-bonds are indicated
(dashed lines).
is non-functional in its apo-form and cannot be reactivated after zinc chela-
tion.
30
The S1 pocket that interacts with the substrate P1 residue provides the
molecular basis for PfA-M1 substrate promiscuity with polar amino-acid-
binding partners explaining the enzyme's ability to cleave a P1 Lys or Arg
residue as well as the smaller hydrophobic amino acids. The entrance to the
specificity pocket is lined by hydrophobic residues (including Val
459
, Tyr
575
,
and Met
1034
), and a polar residue (Glu
572
) is located at the base of the pocket
where it would be available to form an ionic interaction with the side-chain of a
P1 Arg/Lys side-chain. The S1
0
specificity pocket is smaller, more hydrophobic,
and lined by residues Thr
492
, Val
493
, and Val
523
.
7.2.2 PfA-M17 Leucyl Aminopeptidase
The Leucyl aminopeptidase gene is present in a single copy and translates as a
605-amino-acid protein; it is a member of the clan MF, family M17 (http://
merop.sanger.uk) leucine aminopeptidases and thus known as PfA-M17 or
PfLAP. The predicted full-length protein is 68 kDa in size; however, like all
members of the LAP superfamily, PfA-M17 is functional as a homohexamer.
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The full-length amino acid sequence of PfA-M17 also exhibits 480% sequence
similarity with orthologues of the various rodent malaria species (P. berghei,
P. chabaudi chabaudi, and P. yoelii).
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The Plasmodium enzymes are longer than
the canonical members of the LAP family due to an N-terminal extension
containing an asparagine-rich low-complexity region (residues 1-83). The
enzyme sequences are most divergent in this region.
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7.2.2.1 X-Ray Crystal Structure of PfA-M17
The PfA-M17 monomer shares the common LAP structure of a bi-lobed
protomer that contains an N-terminal regulatory domain and a highly conserved
