The amino acid composition of a protein influences its expression

The quantity of each protein in a cell only is only partially correlated with its gene transcription rate. Independent influences on protein synthesis levels include mRNA sequence motifs, amino acyl-tRNA synthesis levels, elongation factor action, and protein susceptibility to degradation. Here we report two novel forms of interaction between the amino acid composition of a protein and its expression level. In animals, the differing origins of amino acids define a nutritional classification system and indicate their potential for scarcity - essential amino acids (EAA) are solely obtained from dietary supply, non-essential amino acids (NEAA) from biosynthetic supply, and conditionally essential amino acids (CEAA) from both. Accessing public proteomic datasets, we demonstrate that CEAA sequence composition is inversely correlated with expression - a rule of supply that is further magnified by rapid cellular proliferation. Similarly, proteins with the most extreme compositions of EAA are reduced in abundance. Homeostatic responses to malnutrition may result from the reductions in expression of extreme composition proteins participating in biological systems such as taste and food-seeking behaviour, oxidative phosphorylation, and chemokine function. The rule can also influence general human phenotypes and disease susceptibility: stature proteins are enriched in CEAAs, and a curated dataset of over 700 cancer proteins is significantly under-represented in EAAs. A second rule, whereby individual amino acids influence protein expression is also described. This rule is shared across all kingdoms of life and rooted in the immutable structural and encoding parameters of each amino acid. Species-specific environmental survival pathways are shown to be enriched in proteins with amino acid compositions favouring higher expression according to this rule. These two rules of protein expression regulation promise new insights into systems biology, evolutionary studies, experimental research design, and public health intervention.