Symmetry facilitated the evolution of heterospecificity and high- order stoichiometry in vertebrate hemoglobin

• 成果类型: Article
• 署名作者: Cortez-Romero, Carlos R.; Lyu, Jixing; Pillai, Arvind S.; Laganowsky, Arthur; Thornton, Joseph W.
• 署名单位: University of Chicago; Texas A&M University System; Texas A&M University College Station; University of Chicago; University of Washington; University of Washington Seattle; University of Chicago
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-13389
• DOI: 10.1073/pnas.2414756122
• 发表日期: 2025-01-28
• 关键词: increased complexity; mass-spectrometry; gene duplication; specificity; mechanisms; principles; proteins; evolve

摘要

Many proteins form paralogous multimers-molecular complexes in which evolutionarily related proteins are arranged into specific quaternary structures. Little is known about the mechanisms by which they acquired their stoichiometry (the number of total subunits in the complex) and heterospecificity (the preference of subunits for their paralogs rather than other copies of the same protein). Here, we use ancestral protein reconstruction and biochemical experiments to study historical increases in stoichiometry and specificity during the evolution of vertebrate hemoglobin (Hb), an alpha 2f32 heterotetramer that evolved from a homodimeric ancestor after a gene duplication. We show that the mechanisms for this evolutionary transition were simple. One hydrophobic substitution in subunit f3 after the gene duplication was sufficient to cause the ancestral dimer to homotetramerize with high affinity across a new interface. During this same interval, a single- residue deletion in subunit alpha at the older interface conferred specificity for the heterotetrameric form and the trans- orientation of subunits within it. These sudden transitions in stoichiometry and specificity were possible because the interfaces in Hb are isologous, binding via the same surface patch on interacting subunits, but rotated 180 degrees relative to each other. This architecture amplifies the impacts of individual mutations on stoichiometry and specificity, especially in higher- order complexes, and allows single substitutions to differentially affect heteromeric and homomeric interactions. Our findings suggest that elaborate and specific symmetrical molecular complexes may often evolve via simple genetic and physical mechanisms.