Novel leucine rich repeats
Hiroki Miyashita, Yoshio Kuroki and Norio Matsushima
Sapporo Medical University, Japan.
Leucine rich repeats (LRRs) are present in over 20,000 proteins from
viruses to eukaryotes. Two to sixty-two LRRs occur in tandem. Each repeat
is typically 20-30 residues long and can be divided into an HCS (Highly
conserved segment) and a VS (Variable segment). The HCS part consists of
an eleven or a twelve residue stretch, LxxLxLxxNx(x/-)L, in which "L" is Leu,
Ile, Val, or Phe, "N" is Asn, Thr, Ser, or Cys, "x" is a non-conserved
residue, and "-" is a possible deletion site. Eight classes have been
recognized. However, there are many unclassified or unrecognized LRRs.
Here we performed to search novel LRRs using protein sequence database.
The novelLRR domains are present over three hundred proteins, which include
fungal ECM33 protein and Monosiga brevicollis LRR receptor kinase, from
unicellular eukaryotes and bacteria. The HCS part is clearly different from
that of the known LRRs and consists of a twelve or a thirteen residue
stretch, VxGx(L/F)x(L/C)xxNx(x/-)L, that is characterized by the addition
of Gly between the first conserved Val and the second conserved Leu. The
novel LRRs identified here form a new family. The novel LRR domains were
classified into four classes. The VS parts of the two classes are consistent
with those of known, normal "SDS22-like" and "IRREKO" classes, while the
other two classes have unique VS parts. The structures, functions, and
evolution of the novel LRR domains and their proteins are described.
The present results should stimulate various experimental studies.