Tbeta 4 is not a simple G-actin sequestering protein and interacts with F-actin at high concentration.

Carlier MF, Didry D, Erk I, Lepault J, Van Troys ML, Vandekerckhove J, Perelroizen I, Yin H, Doi Y, Pantaloni D

The Journal of biological chemistry1 Apr 1996Cited by 59 (Europe PMC)

PMID8621582DOI10.1074/jbc.271.16.9231PepBankPUB-08621582

Summary

Thymosin beta 4 is acknowledged as a major G-actin binding protein maintaining a pool of unassembled actin in motile vertebrate cells. We have examined the function of Tbeta 4 in actin assembly in the high range of concentrations (up to 300 micron) at which Tbeta 4 is found in highly motile blood cells. Tbeta 4 behaves as a simple G-actin sequestering protein only in a range of low concentrations (<20 micron). As the concentration of Tbeta 4 increases, its ability to depolymerize F-actin decreases, due to its interaction with F-actin. The Tbeta 4-actin can be incorporated, in low molar ratios, into F-actin, and can be cross-linked in F-actin using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. As a result of the copolymerization of actin and Tbeta 4-actin complex, the critical concentration is the sum of free G-actin and Tbeta 4-G-actin concentrations at steady state, and the partial critical concentration of G-actin is decreased by Tbeta 4-G-actin complex. The incorporation of Tbeta 4-actin in F-actin is associated to a structural change of the filaments and eventually leads to their twisting around each other. In conclusion, Tbeta 4 is not a simple passive actin-sequestering agent, and at high concentrations the ability of Tbeta 4-actin to copolymerize with actin reduces the sequestering activity of G-actin-binding proteins. These results question the evaluation of the unassembled actin in motile cells. They account for observations made on living fibroblasts overexpressing beta-thymosins.

CC BYText from Europe PMC. Highlighted sentences are the source of results.

Results from this study5

5 results from studies that gave the peptide. No result from this study comes from people.

01LabIn vitro (cell-free)Activity measurement
Thymosin beta‑4 behaves as a simple G-actin sequestering protein only at low concentrations (below 20 micron).
In plain wordsIn lab tests, thymosin beta‑4 acted as a simple actin binder only at low concentrations.
Peptide
Thymosin beta-4 (human)
Outcome
Not applicableG-actin sequestering at low concentrations
Study
n: not reported in source
purified proteins
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Measurements
concentration range of simple G-actin sequestering
< 20 micron
Tbeta 4
Source sentences
Summary
Tbeta 4 behaves as a simple G-actin sequestering protein only in a range of low concentrations (<20 micron).
1 context sentence(design, population, supporting numbers)
Summary · context
We have examined the function of Tbeta 4 in actin assembly in the high range of concentrations (up to 300 micron) at which Tbeta 4 is found in highly motile blood cells.
Show in the study text Report a problemFND-0862158201
02LabIn vitro (cell-free)Activity measurement
As the concentration of thymosin beta‑4 increases, its ability to depolymerize F-actin decreases, due to its interaction with F-actin.
In plain wordsIn lab tests, higher thymosin beta‑4 concentrations made it less able to break down actin filaments.
Peptide
Thymosin beta-4 (human)
Outcome
DecreaseF-actin depolymerization at increasing concentration
Study
n: not reported in source
purified proteins
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
As the concentration of Tbeta 4 increases, its ability to depolymerize F-actin decreases, due to its interaction with F-actin.
1 context sentence(design, population, supporting numbers)
Summary · context
We have examined the function of Tbeta 4 in actin assembly in the high range of concentrations (up to 300 micron) at which Tbeta 4 is found in highly motile blood cells.
Show in the study text Report a problemFND-0862158202
03LabIn vitro (cell-free)Activity measurement
The Tbeta 4-actin complex can be incorporated, in low molar ratios, into F-actin and can be cross-linked in F-actin.
In plain wordsIn lab tests, the thymosin beta‑4-actin complex could join actin filaments in small amounts.
Peptide
Thymosin beta-4 (human)
Outcome
Not applicableIncorporation of Tbeta 4-actin into F-actin
Study
n: not reported in source
purified proteins
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
The Tbeta 4-actin can be incorporated, in low molar ratios, into F-actin, and can be cross-linked in F-actin using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide.
1 context sentence(design, population, supporting numbers)
Summary · context
We have examined the function of Tbeta 4 in actin assembly in the high range of concentrations (up to 300 micron) at which Tbeta 4 is found in highly motile blood cells.
Show in the study text Report a problemFND-0862158203
04LabIn vitro (cell-free)Activity measurement
Copolymerization of actin and the Tbeta 4-actin complex made the critical concentration the sum of free G-actin and Tbeta 4-G-actin, and the Tbeta 4-G-actin complex decreased the partial critical concentration of G-actin.
In plain wordsIn lab tests, joining of the thymosin beta‑4-actin complex into filaments lowered the free actin level needed for assembly.
Peptide
Thymosin beta-4 (human)
Outcome
DecreaseCritical concentration of actin with Tbeta 4-actin copolymerization
Study
n: not reported in source
purified proteins
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
As a result of the copolymerization of actin and Tbeta 4-actin complex, the critical concentration is the sum of free G-actin and Tbeta 4-G-actin concentrations at steady state, and the partial critical concentration of G-actin is decreased by Tbeta 4-G-actin complex.
1 context sentence(design, population, supporting numbers)
Summary · context
We have examined the function of Tbeta 4 in actin assembly in the high range of concentrations (up to 300 micron) at which Tbeta 4 is found in highly motile blood cells.
Show in the study text Report a problemFND-0862158204
05LabIn vitro (cell-free)Mechanism
Incorporation of Tbeta 4-actin in F-actin is associated with a structural change of the filaments that eventually leads to their twisting around each other.
In plain wordsIn lab tests, adding the thymosin beta‑4-actin complex to filaments changed their shape and made them twist together.
Peptide
Thymosin beta-4 (human)
Outcome
Not applicableStructural change of F-actin filaments after Tbeta 4-actin incorporation
Study
n: not reported in source
purified proteins
Outcome group
Receptor activity and mechanism · Pharmacology
Studied dose
Dose not stated
Source sentences
Summary
The incorporation of Tbeta 4-actin in F-actin is associated to a structural change of the filaments and eventually leads to their twisting around each other.
1 context sentence(design, population, supporting numbers)
Summary · context
We have examined the function of Tbeta 4 in actin assembly in the high range of concentrations (up to 300 micron) at which Tbeta 4 is found in highly motile blood cells.
Show in the study text Report a problemFND-0862158205

AI wrote and checked these results. AI can make mistakes, so check important results against the source.

Version history

PepBank keeps every version of the data on this study. Status changes from Retraction Watch, Europe PMC and Crossref are listed with their source.

Version 2Current
13 Oct 2026, 01:52 UTC
Study results updated
Version 1
12 Oct 2026, 18:17 UTC
First added · source update from Europe PMC

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