Direct evidence of the molecular basis for biological silicon transport.
Diatoms are an important group of eukaryotic algae with a curious evolutionary innovation: they sheath themselves in a cell wall made largely of silica. The cellular machinery responsible for silicification includes a family of membrane permeases that recognize and actively transport the soluble precursor of biosilica, silicic acid. However, the molecular basis of silicic acid transport remains obscure. Here, we identify experimentally tractable diatom silicic acid transporter (SIT) homologues and study their structure and function in vitro, enabled by the development of a new fluorescence method for studying substrate transport kinetics. We show that recombinant SITs are Na(+)/silicic acid symporters with a 1:1 protein: substrate stoichiometry and KM for silicic acid of 20 μM. Protein mutagenesis supports the long-standing hypothesis that four conserved GXQ amino acid motifs are important in SIT function. This marks a step towards a detailed understanding of silicon transport with implications for biogeochemistry and bioinspired materials.
School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
Michael J
MJ
Knight
School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
Laura
L
Senior
School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
Bethany
B
Nancolas
School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
Sarah
S
Ratcliffe
School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.|BrisSynBio, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK.
Paul
P
Curnow
D000595:Amino Acid Sequence; D005075:Biological Evolution; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D003001:Cloning, Molecular; D030541:Databases, Genetic; D017377:Diatoms / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D005822:Genetic Vectors / Q000737:chemistry / Q000378:metabolism; D010802:Phylogeny; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012824:Silicic Acid / Q000378:metabolism*; D012825:Silicon / Q000378:metabolism*; D019345:Zinc Acetate / Q000494:pharmacology; D019287:Zinc Sulfate / Q000494:pharmacology
D002352:Carrier Proteins; D011994:Recombinant Proteins; D012824:Silicic Acid; D019287:Zinc Sulfate; D019345:Zinc Acetate; D012825:Silicon