Journal article
The evolutionary appearance of non-cyanogenic hydroxynitrile glucosides in the Lotus genus is accompanied by the substrate specialization of paralogous beta-glucosidases resulting from a crucial amino acid substitution
Lotus japonicus, like several other legumes, biosynthesizes the cyanogenic alpha-hydroxynitrile glucosides lot-australin and linamarin. Upon tissue disruption these compounds are hydrolysed by a specific beta-glucosidase, resulting in the release of hydrogen cyanide. Lotus japonicus also produces the non-cyanogenic gamma- and beta-hydroxynitrile glucosides rhodiocyanoside A and D using a biosynthetic pathway that branches off from lotaustralin biosynthesis.
We previously established that BGD2 is the only beta-glucosidase responsible for cyanogenesis in leaves. Here we show that the paralogous BGD4 has the dominant physiological role in rhodiocyanoside degradation. Structural modelling, site-directed mutagenesis and activity assays establish that a glycine residue (G211) in the aglycone binding site of BGD2 is essential for its ability to hydrolyse the endogenous cyanogenic glucosides.
The corresponding valine (V211) in BGD4 narrows the active site pocket, resulting in the exclusion of non-flat substrates such as lotaustralin and linamarin, but not of the more planar rhodiocyanosides. Rhodiocyanosides and the BGD4 gene only occur in L. japonicus and a few closely related species associated with the Lotus corniculatus clade within the Lotus genus.
This suggests the evolutionary scenario that substrate specialization for rhodiocyanosides evolved from a promiscuous activity of a progenitor cyanogenic beta-glucosidase, resembling BGD2, and required no more than a single amino acid substitution.
Language: | English |
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Year: | 2014 |
Pages: | 299-311 |
ISSN: | 1365313x and 09607412 |
Types: | Journal article |
DOI: | 10.1111/tpj.12561 |
ORCIDs: | Abou Hachem, Maher , 0000-0002-2275-0596 , 0000-0002-3252-3119 , 0000-0001-5828-1018 and 0000-0001-6960-672X |
03502, Genetics - General 03504, Genetics - Plant 10064, Biochemistry studies - Proteins, peptides and amino acids 10802, Enzymes - General and comparative studies: coenzymes 12002, Physiology - General 51518, Plant physiology - Enzymes 51526, Plant physiology - General and miscellaneous AGLYCONE SPECIFICITY BIOSYNTHETIC GENES Biochemistry and Molecular Biophysics CRYSTAL-STRUCTURE Chemical Coordination and Homeostasis Dicotyledones Angiospermae Spermatophyta Plantae (Angiosperms, Dicots, Plants, Spermatophytes, Vascular Plants) - Leguminosae [26260] Lotus japonicus species Enzymology JAPONICUS Lotus burttii Lotus corniculatus Lotus filicaulis Lotus japonicus Lotus japonicus BGD4 gene [Leguminosae] expression, transcription Lotus krylovii MAXIMUM-LIKELIHOOD Molecular Genetics O-METHYLTRANSFERASES PLANT REVERSE GENETICS SESQUITERPENE SYNTHASES SORGHUM WHITE CLOVER australine 118396-02-4 beta-glucosidase beta-glucosidase 9001-22-3 EC 3.2.1.21 bete-hydroxynitrile glucosides rhodiocyanoside A signaling bete-hydroxynitrile glucosides rhodiocyanoside D signaling crucial amino acid cyanogenesis enzyme activity enzyme evolution evolutionary scenario genbank sequence data hydrogen cyanide 74-90-8 hydroxynitrile glucosides leaf linamarin 554-35-8 rhodiocyanosides valine 516-06-3 β–glucosidase