Ion-dependent Polymerization Differences between Mammalian β- and γ-Nonmuscle Actin Isoforms

Sarah E Bergeron; Mei Zhu; Suzanne M Thiem; Karen H Friderici; Peter A Rubenstein

doi:10.1074/jbc.M110.110130

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Ion-dependent Polymerization Differences between Mammalian β- and γ-Nonmuscle Actin Isoforms

Journal article

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Ion-dependent Polymerization Differences between Mammalian β- and γ-Nonmuscle Actin Isoforms

Sarah E Bergeron, Mei Zhu, Suzanne M Thiem, Karen H Friderici and Peter A Rubenstein

The Journal of biological chemistry, Vol.285(21), pp.16087-16095

05/21/2010

DOI: 10.1074/jbc.M110.110130

PMCID: PMC2871477

PMID: 20308063

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Abstract

β- and γ-nonmuscle actins differ by 4 amino acids at or near the N terminus and distant from polymerization interfaces. β-Actin contains an Asp 1 -Asp 2 -Asp 3 and Val 10 whereas γ-actin has a Glu 1 -Glu 2 -Glu 3 and Ile 10 . Despite these small changes, conserved across mammals, fish, and birds, their differential localization in the same cell suggests they may play different roles reflecting differences in their biochemical properties. To test this hypothesis, we established a baculovirus-driven expression system for producing these actins in isoform-pure populations although contaminated with 20–25% insect actin. Surprisingly, Ca-γ-actin exhibits a slower monomeric nucleotide exchange rate, a much longer nucleation phase, and a somewhat slower elongation rate than β-actin. In the Mg-form, this difference between the two is much smaller. Ca-γ-actin depolymerizes half as fast as does β-actin. Mixing experiments with Ca-actins reveal the two will readily co-polymerize. In the Ca-form, phosphate release from polymerizing β-actin occurs much more rapidly and extensively than polymerization, whereas phosphate release lags behind polymerization with γ-actin. Phosphate release during treadmilling is twice as fast with β- as with γ-actin. With Mg-actin in the initial stages, phosphate release for both actins correlates much more closely with polymerization. Calcium bound in the high affinity binding site of γ-actin may cause a selective energy barrier relative to β-actin that retards the equilibration between G- and F-monomer conformations resulting in a slower polymerizing actin with greater filament stability. This difference may be particularly important in sites such as the γ-actin-rich cochlear hair cell stereocilium where local m m calcium concentrations may exist.

Cytoskeleton

Cell Biology

Protein Structure and Folding

Calcium

Actin

Microfilaments

Ion Dependence

Polymerization

Nucleotide Exchange

ATPases

Isoactins

Nonmuscle Cell

Details

Title: Subtitle: Ion-dependent Polymerization Differences between Mammalian β- and γ-Nonmuscle Actin Isoforms
Creators: Sarah E Bergeron - From the
Mei Zhu - Michigan State University
Suzanne M Thiem - the Departments of
Karen H Friderici - the Departments of
Peter A Rubenstein - From the
Resource Type: Journal article
Publication Details: The Journal of biological chemistry, Vol.285(21), pp.16087-16095
DOI: 10.1074/jbc.M110.110130
PMID: 20308063
PMCID: PMC2871477
NLM abbreviation: J Biol Chem
ISSN: 0021-9258
eISSN: 1083-351X
Publisher: American Society for Biochemistry and Molecular Biology; 9650 Rockville Pike, Bethesda, MD 20814, U.S.A
Grant note: DC008803; DC004568 / National Institutes of Health
Language: English
Date published: 05/21/2010
Academic Unit: Stead Family Department of Pediatrics; Biochemistry and Molecular Biology; Internal Medicine
Record Identifier: 9984024417902771

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