Abstract:
:To explain the effect of profilin on actin critical concentration in a manner consistent with thermodynamic constraints and available experimental data, we built a thermodynamically rigorous model of actin steady-state dynamics in the presence of profilin. We analyzed previously published mechanisms theoretically and experimentally and, based on our analysis, suggest a new explanation for the effect of profilin. It is based on a general principle of indirect energy coupling. The fluctuation-based process of exchange diffusion indirectly couples the energy of ATP hydrolysis to actin polymerization. Profilin modulates this coupling, producing two basic effects. The first is based on the acceleration of exchange diffusion by profilin, which indicates, paradoxically, that a faster rate of actin depolymerization promotes net polymerization. The second is an affinity-based mechanism similar to the one suggested in 1993 by Pantaloni and Carlier although based on indirect rather than direct energy coupling. In the model by Pantaloni and Carlier, transformation of chemical energy of ATP hydrolysis into polymerization energy is regulated by direct association of each step in the hydrolysis reaction with a corresponding step in polymerization. Thus, hydrolysis becomes a time-limiting step in actin polymerization. In contrast, indirect coupling allows ATP hydrolysis to lag behind actin polymerization, consistent with experimental results.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Yarmola EG,Dranishnikov DA,Bubb MRdoi
10.1529/biophysj.108.134569subject
Has Abstractpub_date
2008-12-15 00:00:00pages
5544-73issue
12eissn
0006-3495issn
1542-0086pii
S0006-3495(08)81976-5journal_volume
95pub_type
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