Hand-to-Hand Model Referee: 'The conclusion: is that tropomyosin and troponin can move from one set of actin filaments to another at a rate faster than free diffusion in water (by two orders of magnitude!). Surely the author must have considered that this was unlikely for two tightly-binding proteins (in my experience the dissociation of tropomyosin from actin filaments has a half life of many minutes)'. It is really good objection which destroy any hope that dissociation step---free tropomyosin molecule in solution---is included in fast tropomyosin diffusion. But why this step is so inevitable? It is only one power which can take away tropomyosin from actin---another actin filament having free binding sites for tropomyosin. It is real competitor if its affinity to tropomyosin is higher then affinity of actin filament saturated by tropomyosin. This mechanism is illustrated by the Fig. 1 (myosin molecules are not shown).
Fig. 1. Hand-to-hand model (H2H-model) for tropomyosin diffusion on the border of two gel particle, natural actomyosin and desensitized one.
As a consequence of the H2H-model the semiconductory model could be regarded for interaction of two gel particles. See Fig. 2.
Fig. 2. The semiconductory model for fast tropomyosin diffusion in two-component actomyosin suspension or in two-layer system.
This discussion is related to the paper: V.V. Matveev. Evidence of a new type of
protein-protein interaction: desensitized actomyosin blocks Ca2+-sensitivity
of the natural one. A possible model for an intracellular signalling
system related to actin filaments. |
