Selectivity of the surface binding site (SBS) on barley starch synthase I

Casper Wilkens, Jose A. Cuesta-Seijo, Monica Palcic, Birte Svensson

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    Starch synthase I (SSI) from various sources has been shown to preferentially elongate branch chains of degree of polymerisation (DP) from 6–7 to produce chains of DP 8–12. In the recently determined crystal structure of barley starch synthase I (HvSSI) a so-called surface binding site (SBS) was seen, which was found by mutational analysis to be essential for the activity of HvSSI on glycogen. We now show in binding studies using surface plasmon resonance that HvSSI has no detectable affinity for malto-triose and -tetraose, but clearly binds maltopentaose, -hexaose, -heptaose (M7) and β-cyclodextrin (β-CD) albeit with a measurable K D for only β-CD and M7. Moreover, an HvSSI SBS mutant F538A lost the ability to bind β-CD and maltooligosaccharides. This behaviour suggests that a chain in the α-glucan molecule (amylopectin) that is undergoing extension attaches itself at the SBS and that the active site itself, likely working on a different end chain, has low affinity for both substrate and product.
    Original languageEnglish
    JournalBiologia
    Volume69
    Issue number9
    Pages (from-to)1118-1121
    Number of pages4
    ISSN0006-3088
    DOIs
    Publication statusPublished - 2014

    Keywords

    • surface binding site
    • starch synthase I
    • barley
    • surface plasmon resonance
    • β-cyclodextrin
    • maltooligosaccharides

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