The Sema domain can be found associated with other domains such as PSI, IPT,
Ig-like and TSP1 (see <PDOC50092>) [1,2].
The Sema domain is characterized by a conserved set of cysteine residues,
which form four disulfide bonds to stabilize the structure. The Sema domain
fold is a variation of the β propeller topology, with seven blades radially
arranged around a central axis (see <PDB:1Q47>). Each blade contains a four-stranded (strands A to D) antiparallel β sheet. The inner strand of each
blade (A) lines the channel at the center of the propeller, with strands B and
C of the same repeat radiating outward, and strand D of the next repeat
forming the outer edge of the blade. The large size of the Sema domain is not
due to a single inserted domain but results from the presence of additionnal
secondary structure elements inserted in most of the blades. The Sema domain
uses a 'loop and hook' system to close the circle between the first and the
last blades. The blades are constructed sequentially with an N-terminal β-strand closing the circle by providing the outermost strand (D) of the seventh
(C-terminal) blade. The β-propeller is further stabilized by an extension
of the N-terminus, providing an additional, fifth β-strand on the outer
edge of blade 6 [3,4,5].
The profile we developed covers the entire Sema domain.
August 2004 / First entry.
PROSITE method (with tools and information) covered by this documentation:
Xu X. Ng S. Wu Z.-L. Nguyen D. Homburger S. Seidel-Dugan C. Ebens A. Luo Y.
Human semaphorin K1 is glycosylphosphatidylinositol-linked and defines a new subfamily of viral-related semaphorins.
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