Molecular basis of hemoglobin adaptation in the high-flying bar-headed goose

TY - JOUR

T1 - Molecular basis of hemoglobin adaptation in the high-flying bar-headed goose

AU - Natarajan, Chandrasekhar

AU - Jendroszek, Agnieszka

AU - Kumar, Amit

AU - Weber, Roy E.

AU - Tame, Jeremy R. H.

AU - Fago, Angela

AU - Storz, Jay F.

PY - 2018/4

Y1 - 2018/4

N2 - During the adaptive evolution of a particular trait, some selectively fixed mutations may be directly causative and others may be purely compensatory. The relative contribution of these two classes of mutation to adaptive phenotypic evolution depends on the form and prevalence of mutational pleiotropy. To investigate the nature of adaptive substitutions and their pleiotropic effects, we used a protein engineering approach to characterize the molecular basis of hemoglobin (Hb) adaptation in the high-flying bar-headed goose (Anser indicus), a hypoxia-tolerant species renowned for its trans-Himalayan migratory flights. To test the effects of observed substitutions on evolutionarily relevant genetic backgrounds, we synthesized all possible genotypic intermediates in the line of descent connecting the wildtype bar-headed goose genotype with the most recent common ancestor of bar-headed goose and its lowland relatives. Site-directed mutagenesis experiments revealed one major-effect mutation that significantly increased Hb-O-2 affinity on all possible genetic backgrounds. Two other mutations exhibited smaller average effect sizes and less additivity across backgrounds. One of the latter mutations produced a concomitant increase in the autoxidation rate, a deleterious side-effect that was fully compensated by a second-site mutation at a spatially proximal residue. The experiments revealed three key insights: (i) subtle, localized structural changes can produce large functional effects; (ii) relative effect sizes of functionaltering mutations may depend on the sequential order in which they occur; and (iii) compensation of deleterious pleiotropic effects may play an important role in the adaptive evolution of protein function.

AB - During the adaptive evolution of a particular trait, some selectively fixed mutations may be directly causative and others may be purely compensatory. The relative contribution of these two classes of mutation to adaptive phenotypic evolution depends on the form and prevalence of mutational pleiotropy. To investigate the nature of adaptive substitutions and their pleiotropic effects, we used a protein engineering approach to characterize the molecular basis of hemoglobin (Hb) adaptation in the high-flying bar-headed goose (Anser indicus), a hypoxia-tolerant species renowned for its trans-Himalayan migratory flights. To test the effects of observed substitutions on evolutionarily relevant genetic backgrounds, we synthesized all possible genotypic intermediates in the line of descent connecting the wildtype bar-headed goose genotype with the most recent common ancestor of bar-headed goose and its lowland relatives. Site-directed mutagenesis experiments revealed one major-effect mutation that significantly increased Hb-O-2 affinity on all possible genetic backgrounds. Two other mutations exhibited smaller average effect sizes and less additivity across backgrounds. One of the latter mutations produced a concomitant increase in the autoxidation rate, a deleterious side-effect that was fully compensated by a second-site mutation at a spatially proximal residue. The experiments revealed three key insights: (i) subtle, localized structural changes can produce large functional effects; (ii) relative effect sizes of functionaltering mutations may depend on the sequential order in which they occur; and (iii) compensation of deleterious pleiotropic effects may play an important role in the adaptive evolution of protein function.

KW - SPERM-WHALE MYOGLOBIN

KW - HIGH-ALTITUDE

KW - LIGAND-BINDING

KW - ESCHERICHIA-COLI

KW - ANSER-INDICUS

KW - COMPENSATORY MUTATIONS

KW - ALLOSTERIC MECHANISM

KW - THEORETICAL-ANALYSIS

KW - DISTAL HISTIDINE

KW - OXYGEN-AFFINITY

U2 - 10.1371/journal.pgen.1007331

DO - 10.1371/journal.pgen.1007331

M3 - Journal article

C2 - 29608560

SN - 1553-7390

VL - 14

JO - P L o S Genetics

JF - P L o S Genetics

IS - 4

M1 - e1007331

ER -