ProX from marine Synechococcus spp. show a sole preference for glycine‐betaine with differential affinity between ecotypes

Osmotic stress, caused by high or fluctuating salt concentrations, is a crucial abiotic factor affecting microbial growth in aquatic habitats. Many organisms utilize common responses to osmotic stress, generally requiring active extrusion of toxic inorganic ions and accumulation of compatible solute...

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Bibliographic Details
Published in:Environmental microbiology 2022-12, Vol.24 (12), p.6071-6085
Main Authors: Ford, Benjamin A., Ranjit, Pramita, Mabbutt, Bridget C., Paulsen, Ian T., Shah, Bhumika S.
Format: Article
Language:English
Subjects:
Abiotic factors
Affinity
Aquatic habitats
Betaine - metabolism
Binding
Biocompatibility
Ecotype
Ecotypes
Glycine
Glycine (amino acid)
Glycine - metabolism
Glycine betaine
Ionic strength
Microorganisms
Osmoprotectants
Osmosis
Osmotic stress
Phylogenetics
Phylogeny
Proline
Proteins
Regulatory mechanisms (biology)
Solutes
Specificity
Synechococcus
Synechococcus - genetics
Synechococcus - metabolism
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Summary:Osmotic stress, caused by high or fluctuating salt concentrations, is a crucial abiotic factor affecting microbial growth in aquatic habitats. Many organisms utilize common responses to osmotic stress, generally requiring active extrusion of toxic inorganic ions and accumulation of compatible solutes to protect cellular machinery. We heterologously expressed and purified predicted osmoprotectant, proline/glycine betaine‐binding proteins (ProX) from two phylogenetically distinct Synechococcus spp. MITS9220 and WH8102. Homologues of this protein are conserved only among Prochlorococcus LLIV and Synechococcus clade I, III and CRD1 strains. Our biophysical characterization show Synechococcus ProX exists as a dimer, with specificity solely for glycine betaine but not to other osmoprotectants tested. We discovered that MITS9220_ProX has a 10‐fold higher affinity to glycine betaine than WH8102_ProX, which is further elevated (24‐fold) in high salt conditions. The stronger affinity and effect of ionic strength on MITS9220_ProX glycine betaine binding but not on WH8102_ProX alludes to a novel regulatory mechanism, providing critical functional insights into the phylogenetic divergence of picocyanobacterial ProX proteins that may be necessary for their ecological success.
ISSN:1462-2912
1462-2920
DOI:10.1111/1462-2920.16168