Physical limits on computation by assemblies of allosteric proteins

TL;DR

This paper investigates the fundamental physical limits on information processing in assemblies of allosteric proteins, exemplified by the TnC-TnI complex, revealing a trade-off between signaling fidelity and deactivation speed.

Contribution

It introduces a phenomenological model showing how local interactions constrain the energy landscape and set an upper bound on processing rates in allosteric protein assemblies.

Findings

Signaling fidelity and deactivation kinetics cannot be optimized simultaneously.

Nearest-neighbor interactions restrict the free energy landscape topology.

There is an upper limit on processing rate due to these physical constraints.

Abstract

Assemblies of allosteric proteins, nano-scale Brownian computers, are the principle information processing devices in biology. The troponin C-troponin I (TnC-TnI) complex, the Ca$^{2+}$-sensitive regulatory switch of the heart, is a paradigm for Brownian computation. TnC and TnI specialize in sensing (reading) and reporting (writing) tasks of computation. We have examined this complex using a newly developed phenomenological model of allostery. Nearest-neighbor-limited interactions among members of the assembly place previously unrecognized constrains the topology of the system's free energy landscape and generate degenerate transition probabilities. As a result, signaling fidelity and deactivation kinetics can not be simultaneously optimized. This trade-off places an upper limit on the rate of information processing by assemblies of allosteric proteins that couple to a single ligand chemical bath.