Disordered Motifs and Domains in Cell Control
Poster Session I
20-POS
Board 20
G-Actin is Quasi-Stationary State Stabilised by Ca Ion, While Polypeptide Chain of Actin
Determines Its Inactivated State
Olga I. Povarova
1
, Vladimir N. Uversky
2,3,4
, Irina M. Kuznetsova
1,5
,
Konstantin K.
Turoverov
1,5
.
1
Institute of Cytology RAS, St.Petersburg, Russian Federation,
2
Morsani College of Medicine,
University of South Florida, Tampa, FL, USA,
3
Institute for Biological Instrumentation RAS,
Pushchino, Russian Federation,
4
Faculty of Science, King Abdulaziz University, Jeddah, Saudi
Arabia,
5
St. Petersburg State Polytechnical University, St.Petersburg, Russian Federation.
Actin is a ubiquitous and multifunctional protein. It is one of the main components of the system
of muscle contraction, it forms the cytoskeleton, it is found in the cell nucleus in which, except
for the motility and scaffold functions, actin acts as a regulator protein that participates in the
processes of transcription and chromatin remodeling. From one hand G-actin is surely globular
protein, it is even called so, yet by multifunctionality and ubiquity it resembles intrinsically
disordered proteins. So what is it? Careful consideration of the unfolding-folding behavior of G-
actin was a crucial step for answering this question. EDTA-induced calcium removal from actin
and action of various denaturing agents (pH, temperature, and chemical denaturants), all result in
the formation of the so-called inactivated actin (I-actin), which is a complex compact oligomer
containing 14-16 subunits. G-actin denaturation in vitro is a completely irreversible process.
Therefore, I-actin represents the thermodynamically stable state of a polypeptide chain,
information about which is encoded in the amino acid sequence of this protein. Although it is
believed that I-actin is functionally inactive, one cannot exclude a possibility that the functional
importance of this form of actin is not established as of yet. G-actin, represents a
thermodynamically instable, quasi-stationary state, which is formed in vivo as a result of
complex posttranslational energy-intensive folding events controlled and driven by cellular
folding machinery.
This work was supported by Program MCB RAS, grant RSF 14-24-00131
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