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Figure 1.
Overall structure of IREM-1, features of the extended protrusion and
comparison with CLM-1. (a) A ribbon representation of the IREM-1
structure. IREM-1 has the expected V-set Ig domain fold present in the
immunoglobulins. The secondary structure elements (β-strands and
the 310 α-helix) were defined using the program
DSSP.41 The
antibody's equivalent CDR loops (CDReq) are shown in red and are
labelled. Disulphide bonds are shown and are labelled with their
respective cysteine residues. In this ribbon representation and in all
the subsequent diagrams, N and C denote the amino terminus and the
carboxy terminus of the protein chain. The location of the potential
N-glycosylation site, which involves asparagine 88, is shown with a
red diamond. (b) An important feature of the IREM-1 structure is the
formation of a prominent protrusion that extends from the main
immunoglobulin body. This protrusion is about 18 Å long,
15 Å wide and 11 Å deep. As seen in this Figure,
the top of this protrusion is blocked, in part, by the side-chains of
tryptophan 59, aspartate 116 and glutamate 111. The other amino acid
residues present at this protrusion are isoleucine 64, lysine 67,
tryptophan 52 and tryptophan 107. (c) Superimposition of IREM-1 with
its murine homologous CLM-1 gives an rmsd of 1.06 for all the
structurally equivalent Cα atoms forming the core of the
immunoglobulin-like domain (102 residues). The orientation of IREM-1
and CLM-1 here is equivalent to that in (a). In this superimposition
diagram, IREM-1 is in blue and CLM-1 is in red. The β-hairpin
formed by β-strands C-C′ is labelled. The location of the
CDReq loops is shown schematically. The circle highlights the
prominent structural difference of the CDReq3 between IREM-1 and
CLM-1.
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