[Paper Review] Amino Acid Distributions and the Effect of Optimal Growth Temperature

Benjamin D. Greenbaum, Pradeep Kumar+1 more|arXiv (Cornell University)|Sep 18, 2013

RNA and protein synthesis mechanisms36 references3 citations

TL;DR

This study analyzes amino acid distributions across diverse organisms, particularly extremophiles, to investigate how optimal growth temperature (OGT) influences sequence composition. Using first-passage distributions to detect long-range residue correlations, it reveals a nearly universal exponential background tied to individual amino acid frequencies and identifies temperature-dependent correlations not previously characterized, especially in relation to molecular weight and codon degeneracy.

ABSTRACT

We perform an exhaustive analysis of genome statistics for organisms, particularly extremophiles, growing in a wide range of physicochemical conditions. Specifically, we demonstrate how the correlation between the frequency of amino acids and their molecular weight, preserved on average, typically decreases as optimal growth temperature increases. We show how the relation between codon degeneracy and amino acid mass is enforced across these organisms. We assess the occurrence of contiguous amino acids, finding several significant short words, often containing cysteine, histidine or proline. Typically, the significance of these words is independent of growth temperature. In a novel approach, first-passage distributions are used to capture correlations between discontiguous residues. We find a nearly universal exponential background that we relate to properties of the aforementioned individual amino acid frequencies. We find this approach reliably extracts correlations that depend on growth temperature, some of which have not been previously characterized.

Motivation & Objective

• To understand how optimal growth temperature (OGT) shapes amino acid composition across diverse organisms.
• To investigate the relationship between amino acid molecular weight, codon degeneracy, and OGT.
• To detect non-random patterns in contiguous and discontiguous amino acid sequences using statistical methods.
• To explore whether sequence correlations beyond local motifs are influenced by environmental adaptation, particularly temperature.
• To develop a novel statistical framework using first-passage distributions to extract biologically meaningful correlations in protein sequences.

Proposed method

• Performed an exhaustive genome-wide analysis of amino acid frequencies across organisms with varying optimal growth temperatures.
• Quantified the correlation between amino acid frequency and molecular weight, observing its decrease with increasing OGT.
• Analyzed the relationship between codon degeneracy and amino acid mass across species to assess evolutionary constraints.
• Identified significant contiguous amino acid motifs, particularly those enriched in cysteine, histidine, and proline, and assessed their independence from OGT.
• Applied first-passage distributions to model correlations between discontiguous residues, capturing long-range sequence dependencies.
• Established a nearly universal exponential background distribution in first-passage statistics, linked to individual amino acid frequencies, as a null model for detecting temperature-sensitive correlations.

Experimental results

Research questions

• RQ1 How does optimal growth temperature influence the correlation between amino acid frequency and molecular weight?
• RQ2 To what extent is the relationship between codon degeneracy and amino acid mass conserved across organisms with different OGTs?
• RQ3 Are there significant non-random patterns in contiguous amino acid sequences that vary with growth temperature?
• RQ4 Can first-passage distributions effectively detect temperature-dependent correlations between discontiguous residues in protein sequences?
• RQ5 What is the nature of the background statistical distribution in first-passage analysis, and how does it relate to individual amino acid frequencies?

Key findings

• The correlation between amino acid frequency and molecular weight decreases significantly with increasing optimal growth temperature.
• The relationship between codon degeneracy and amino acid mass is consistently enforced across diverse organisms, suggesting strong evolutionary constraints.
• Several short contiguous amino acid motifs—especially those rich in cysteine, histidine, and proline—occur with significant overrepresentation, independent of growth temperature.
• A nearly universal exponential background distribution emerges in first-passage analysis, which is directly related to the frequencies of individual amino acids.
• The first-passage approach successfully extracts temperature-dependent correlations between discontiguous residues, including previously uncharacterized patterns.
• The method reveals that long-range residue correlations in protein sequences are modulated by optimal growth temperature, indicating a potential role in protein stability and adaptation.