| Literature References | 1. LIU, C., GILMONT, R.R., BENNDORF, R. AND WELSH, M.J.
Identification and characterization of a novel protein from Sertoli cells,
PASS1, that associates with mammalian small stress protein hsp27.
J.BIOL.CHEM 275(25) 18724-18731 (2000).
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| Documentation | The small heat shock proteins of vertebrates are thought to play a major
role in the cellular response to stress, and appear to play a role in a
range of other physiological activities. Indeed, in response to many forms
of stress, including heat, the expression of heat shock proteins is
increased, and coincidentally these cells become more stress-resistant. One
of these proteins is Heat Shock Protein (hsp) 27, for which 3 hypotheses
currently exist to explain its mechanism of action: (i) it has chaperone-
like activity, serving as a site where denatured, unfolding proteins can
bind until hsp70-dependent refolding can occur; (ii) it stabilises
microfilaments, strengthening the cytoskeleton; and (iii) it enhances
levels of the cellular antioxidant glutathione [1].
It was hypothesised that hsp27 associates with different protein partners
in order to effect its various cellular functions. Thus, a yeast two-hybrid
screen was performed on a rat Sertoli cell cDNA library, which identified a
novel binding protein, termed Protein Associated with Small Stress protein
1 (PASS1). PASS1 is a 428-amino acid protein that, aside from its human
orthologue, shares no significant similarity with known proteins, but does
show 34% identity to a genomic C.elegans sequence. In vitro experiments
confirm the specific association of PASS1 and hsp27, while expression
studies reveal PASS1 to be expressed in several tissues, with highest
levels in the Sertoli cells of the testis. In addition, a smaller mRNA
than the original cDNA isolated from Sertoli cells was found in kidney,
suggesting that alternative splicing may occur. Deletion experiments,
resulting in truncated proteins, revealed the hsp27-association domain to
exist between amino acids 108 and 208 of PASS1. Finally, expression of
PASS1 in cultured cell lines, which do not normally express PASS1,
inhibited the ability of hsp27 to protect the cells against heat shock,
confirming that PASS1 does indeed associate with hsp27 in vivo [1].
PASS1 is a 3-element fingerprint that provides a signature for the PASS1
protein family. The fingerprint was derived from an initial alignment of 3
sequences: the motifs were drawn from conserved regions spanning a short
region of the central portion of the alignment. Two iterations on
SPTR40_20f were required to each convergence, at which point a true set
comprising 4 sequences was identified.
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