The missing link in the fungal D-galacturonate pathway: Identification of the L-threo-3-deoxy-hexulosonate aldolase

Satu Hilditch, Suvi Berghäll, Nisse Kalkkinen, Merja Penttilä, Peter Richard

    Research output: Contribution to journalArticleScientificpeer-review

    39 Citations (Scopus)

    Abstract

    The fungal path for the catabolism of D-galacturonate is only partially known. It is however distinctly different to the wellknown bacterial path. The known elements of the fungal path are D-galacturonate reductase converting D-galacturonate to L-galactonate and L-galactonate dehydratase converting L-galactonate to L-threo-3-deoxy-hexulosonate (2-keto-3-deoxy-L-galactonate). Here we describe the missing link in this pathway, an aldolase converting L-threo-3-deoxy-hexulosonate to pyruvate and L-glyceraldehyde. Fungal enzymes converting L-glyceraldehyde to glycerol have been described previously. The L-threo-3-deoxy-hexulosonate aldolase activity was induced in the mold Hypocrea jecorina (Trichoderma reesei) during growth on D-galacturonate. The enzyme was purified from this mold and a partial amino acid sequence obtained. This sequence was then used to identify the corresponding gene from the H. jecorina genome. The deletion of the gene resulted in a strain unable to grow on D-galacturonate and accumulating L-threo-3-deoxy-hexulosonate. The open reading frame was cloned from cDNA and functionally expressed in the yeast Saccharomyces cerevisiae. A histidine-tagged protein was expressed, purified, and characterized. The enzyme catalyzed reaction was reversible. With L-threo-3-deoxy-hexulosonate as substrate the Km was 3.5 mM and with pyruvate and L-glyceraldehyde the Km were 0.5 and 1.2 mM, respectively.

    Original languageEnglish
    Pages (from-to)26195-26201
    Number of pages7
    JournalJournal of Biological Chemistry
    Volume282
    Issue number36
    DOIs
    Publication statusPublished - 7 Sep 2007
    MoE publication typeA1 Journal article-refereed

    Keywords

    • bacteria (microorganisms)
    • Hypocrea jecorina
    • Saccharomyces cerevisiae
    • Galacturonate reductases
    • Glyceraldehydes
    • Hexulosonate
    • Yeast
    • enzyme activity

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