Optimal receptor-cluster size determined by intrinsic and extrinsic noise

TL;DR

This paper investigates how receptor clustering in bacterial chemotaxis affects sensing accuracy by analyzing the interplay of intrinsic and extrinsic noise, revealing an optimal cluster size that balances signal amplification and noise.

Contribution

It combines the Monod-Wyman-Changeux model with noise calculations to determine optimal receptor cluster size considering different noise sources.

Findings

Clustering offers no advantage under extrinsic noise alone.

Intrinsic signaling noise leads to an optimal receptor complex size.

Optimal sizes align with biological observations in bacteria and eukaryotic cells.

Abstract

Biological cells sense external chemical stimuli in their environment using cell-surface receptors. To increase the sensitivity of sensing, receptors often cluster, most noticeably in bacterial chemotaxis, a paradigm for signaling and sensing in general. While amplification of weak stimuli is useful in absence of noise, its usefulness is less clear in presence of extrinsic input noise and intrinsic signaling noise. Here, exemplified on bacterial chemotaxis, we combine the allosteric Monod-Wyman- Changeux model for signal amplification by receptor complexes with calculations of noise to study their interconnectedness. Importantly, we calculate the signal-to-noise ratio, describing the balance of beneficial and detrimental effects of clustering for the cell. Interestingly, we find that there is no advantage for the cell to build receptor complexes for noisy input stimuli in absence of intrinsic signaling noise. However, with intrinsic noise, an optimal complex size arises in line with estimates of the sizes of chemoreceptor complexes in bacteria and protein aggregates in lipid rafts of eukaryotic cells.