A determinant of substrate specificity predicted from the Acyl-Acyl carrier protein desaturase of developing cat's claw seed

Edgar B. Cahoon, Salehuzzaman Shah, John Shanklin, John Browse

Research output: Contribution to journalArticle

72 Citations (Scopus)

Abstract

Cat's claw (Doxantha unguis-cati L.) vine accumulates nearly 80% palmitoleic acid (16:1Δ9) plus cis-vaccenic acid (18:1Δ11) in its seed oil. To characterize the biosynthetic origin of these unusual fatty acids, cDNAs for acyl-acyl carrier protein (acyl-ACP) desaturases were isolated from developing cat's claw seeds. The predominant acyl-ACP desaturase cDNA identified encoded a polypeptide that is closely related to the stearoyl (Δ9-18:0)-ACP desaturase from castor (Ricinis commuais L.) and other species. Upon expression in Eschcrichia coli, the cat's claw polypeptide functioned as a Δ9 acyl-ACP desaturase but displayed a distinct substrate specificity for palmitate (16:0)-ACP rather than stearate (18:0)-ACP. Comparison of the predicted amino acid sequence of the cat's claw enzyme with that of the castor Δ9-18:0-ACP desaturase suggested that a single amino acid substitution (L118W) might account in large part for the differences in substrate specificity between the two desaturases. Consistent with this prediction, conversion of leucine-118 to tryptophan in the mature castor Δ9-18:0-ACP desaturase resulted in an 80-fold increase in the relative specificity of this enzyme for 16:0-ACP. The alteration in substrate specificity observed in the L118W mutant is in agreement with a crystallographic model of the proposed substrate-binding pocket of the castor Δ9-18:0-ACP desaturase.

Original languageEnglish (US)
Pages (from-to)593-598
Number of pages6
JournalPlant physiology
Volume117
Issue number2
DOIs
StatePublished - Jan 1 1998

Fingerprint

acyl-(acyl-carrier-protein)desaturase
Cat's Claw
acyl carrier protein
claws
substrate specificity
Substrate Specificity
Seeds
cats
seeds
Dolichandra
polypeptides
vaccenic acid
palmitoleic acid
palmitates
amino acid substitution
enzymes
stearic acid
seed oils
tryptophan
vines

ASJC Scopus subject areas

  • Physiology
  • Genetics
  • Plant Science

Cite this

A determinant of substrate specificity predicted from the Acyl-Acyl carrier protein desaturase of developing cat's claw seed. / Cahoon, Edgar B.; Shah, Salehuzzaman; Shanklin, John; Browse, John.

In: Plant physiology, Vol. 117, No. 2, 01.01.1998, p. 593-598.

Research output: Contribution to journalArticle

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