Glycan processing in the Golgi -- optimal information coding and constraints on cisternal number and enzyme specificity

TL;DR

This paper models the Golgi apparatus's glycan processing as an information coding problem, revealing how cisternal number and enzyme specificity constrain the synthesis of complex glycan distributions.

Contribution

It provides a quantitative analysis of how Golgi structure and enzyme specificity influence the fidelity of glycan synthesis, highlighting optimal configurations for complex glycan production.

Findings

Multiple cisternae are required for complex glycan distributions.

Precise enzyme partitioning enhances glycan synthesis fidelity.

There is an optimal enzyme specificity level for target distribution accuracy.

Abstract

Many proteins that undergo sequential enzymatic modification in the Golgi cisternae are displayed at the plasma membrane as cell identity markers. The modified proteins, called glycans, represent a molecular code. The fidelity of this glycan code is measured by how accurately the glycan synthesis machinery realises the desired target glycan distribution for a particular cell type and niche. In this paper, we quantitatively analyse the tradeoffs between the number of cisternae and the number and specificity of enzymes, in order to synthesize a prescribed target glycan distribution of a certain complexity. We find that to synthesize complex distributions, such as those observed in real cells, one needs to have multiple cisternae and precise enzyme partitioning in the Golgi. Additionally, for fixed number of enzymes and cisternae, there is an optimal level of specificity of enzymes that achieves the target distribution with high fidelity. Our results show how the complexity of the target glycan distribution places functional constraints on the Golgi cisternal number and enzyme specificity.