{PDOC51148}
{PS51148; AXH}
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* AXH domain profile *
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The AXH  (ataxin-1  and  HMG-box  protein  1) domain is a module of ~130 amino
acids, which  has  been  identified  in  ATX1  and in the apparently unrelated
transcription factor HBP1 [1]. It is found in many vertebrate and invertebrate
proteins. It  has  been  suggested that the AXH domain is a molecular scaffold
domain engaged in multiple protein-protein interactions and in RNA binding.

The AXH  domain consists of a noncanonical oligonucleotide and oligosaccharide
binding (OB)  fold.  Although  sharing a similar OB fold, the structure of the
AXH domains  from  ATX1  (see  <PDB:1OA8>)  and  HBP1  (see  <PDB:1V06>)  have
genuinely distinct  folds.  The  differences  are  not,  as in other chameleon
sequences, determined  by  a  different  tendency  to adopt distinct secondary
structures: the  two  folds  share  the same secondary structure elements, but
these are  differently  arranged  in  space.  The  AXH  domain has a chameleon
structure in  which  the  N  and  C  termini  can  adopt  distinctly different
conformation. Neither  of  the  differences  are induced by binding to another
molecule. While clearly correlated (sharing a sequence identity of ca. 30% and
a homology  of  ca.  50% depending on the species), AXH has slightly different
domain boundaries and distinct properties in ATX1 and HBP1. There is a cluster
of charged residues that could constitute a ligand-binding site [2,3].

Some proteins known to contain a AXH domain are listed below:

 - Animal   ataxin-1   (ATX1),  a  neurodegenerative  disorder  protein  whose
   glutamine-repeat expanded  form causes spinocerebellar ataxia type 1 (SCA1)
   in humans and exerts cytotoxicity in Drosophila and mouse.
 - Animal Brother of ataxin-1 (Boat) [4].
 - Vetebrate HMG box containing protein 1 (HBP1). It is thought to be involved
   in an   architectural   regulation   of  chromatin  and  in  specific  gene
   expression.

The profile we developed covers the entire AXH domain.

-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: October 2005 / First entry.

[ 1] de Chiara C., Giannini C., Adinolfi S., de Boer J., Guida S.,
     Ramos A., Jodice C., Kioussis D., Pastore A.
     "The AXH module: an independently folded domain common to ataxin-1 and
     HBP1."
     FEBS Lett. 551:107-112(2003).
     PubMed=12965213
[ 2] Chen Y.W., Allen M.D., Veprintsev D.B., Loewe J., Bycroft M.
     "The structure of the AXH domain of spinocerebellar ataxin-1."
     J. Biol. Chem. 279:3758-3765(2004).
     PubMed=14583607; DOI=10.1074/jbc.M309817200
[ 3] de Chiara C., Menon R.P., Adinolfi S., de Boer J., Ktistaki E.,
     Kelly G., Calder L., Kioussis D., Pastore A.
     "The AXH domain adopts alternative folds the solution structure of
     HBP1 AXH."
     Structure 13:743-753(2005).
     PubMed=15893665; DOI=10.1016/j.str.2005.02.016
[ 4] Mizutani A., Wang L., Rajan H., Vig P.J.S., Alaynick W.A., Thaler J.P.,
     Tsai C.-C.
     "Boat, an AXH domain protein, suppresses the cytotoxicity of mutant
     ataxin-1."
     EMBO J. 24:3339-3351(2005).
     PubMed=16121196; DOI=10.1038/sj.emboj.7600785

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