Biology Reference
In-Depth Information
Mutations in the NLS motif of LLA23 contain two defined regions, either
of which is necessary for partial nuclear targeting but both are required for
complete nuclear localization (
Wang et al., 2005
). The putative NLS is also
conserved in other members of ASR proteins both in dicots and in mono-
cots (
Liu et al., 2010
). The reported presence of putative bipartite NLSs in
a high proportion of plant b-ZIP proteins (
Raikhel, 1992
;
Varagona et al.,
1992
) suggests that the bipartite structure may be the most prevalent NLS
configuration in plants across a spectrum of divergent nuclear proteins.
3.2.2. Intrinsically Unstructured Protein
The lily ASR protein is stable at 90 °C for 10 min (
Wang et al., 1996
) and
the boiling-soluble feature is due to its flexible conformation in solution.
The protein contains relatively poor order-promoting amino acid residues
and enriched disorder-promoting amino acid residues that result in the
intrinsically unstructured conformation of the polypeptide (
Dai et al., 2011
;
Goldgur et al., 2007
). Intrinsically unstructured proteins have been found to
play crucial roles despite the lack of certain high-ordered structures (
Dyson
and Wright, 2005
). For example, the unstructured form of ASR1 has
chaperone-like activity that helps stabilize macromolecules against dena-
turation caused by heat and freeze-thaw cycles (
Hsu et al., 2011
;
Konrad
and Bar-Zvi, 2008
). The hydrophilic and boiling-soluble ASR protein may
function as an intracellular water retainer for preventing local dehydration
during stress (
Dai et al., 2011
;
Yang et al., 2005
). Furthermore, the protec-
tive activity of ASR1 is synergistic with glycine-betaine, which accumulates
under unfavorable environmental conditions (
Konrad and Bar-Zvi, 2008
).
In addition, ASR can fold into an ordered structure and form a homodimer
upon binding with zinc ions (
Goldgur et al., 2007
).
Uversky et al. (2000)
indicated that most natively unfolded proteins
have low-mean hydrophobicity, high net charge, and low molecular weight,
with less than 150 amino acid residues. For example, LEA proteins have a
relatively high composition of hydrophilic amino acids, most of which are
disordered under native conditions (
Battaglia et al., 2008
;
Mouillon et al.,
2008
). ASR is another example that fits these criteria. As a hydrophilin,
Battaglia et al. (2008)
classified ASR as a Group 7 LEA protein.
3.2.3. Cellular Localization
Subcellular fractionation experiments and immunodetection in tomato fruit
chromatin fractions suggest that tomato ASR1 is localized in the nucleus
(
Iusem et al., 1993
). Although ASR easily passes through the nuclear pore
Search WWH ::
Custom Search