Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2003
Publication Date: October 1, 2003
Citation: Salvucci, M.E. 2003. Distinct sucrose isomerases catalyze trehalulose synthesis in whiteflies, bemisia argentifolii, and erwina rhapontici. Comparative Biochemistry and Physiology. 135B: 385-395. Interpretive Summary: The silverleaf whitefly (Bemisia argentifolii) is a serious pest, causing severe damage to a variety of crop species including cotton. Whiteflies feed on the conductive-tissue of plants deriving nutrition from the sugars and amino acids from the plant sap. Because of the high sugar content of plant sap, sugar is in excess and some must be excreted in the form of a sugary mixture called honeydew. One of the major sugars in honeydew is an unusual isomer of sucrose called trehalulose, produced by an enzyme called trehalulose synthase. Since trehalulose is a commercially valuable sugar, we isolated and characterized trehalulose synthase from whiteflies and compared its properties to those of a well-characterized trehalulose-producing enzyme from the bacterium, Erwinia rhapontici. The results showed that trehalulose synthase from whiteflies was structurally and functionally different from the trehalulose-producing enzyme from bacteria. The properties of the whitefly trehalulose synthase make it a good candidate for use in the commercial production of trehalulose, either by using the immobilized enzyme or after expressing the transgene in sugar-accumulating plants like sugarcane or sugar beet.
Technical Abstract: Isomaltulose and trehalulose are commercially valuable sucrose-substitutes that are produced in several microorganisms by the pall gene product, a sucrose isomerase. Trehalulose also occurs in the silverleaf whitefly, Bemisia argentifoli, as the major carbohydrate in the honeydew. To determine if the enzyme that synthesizes trehalulose in whiteflies was similar to the wellcharacterized sucrose isomerase from microbial sources, the properties of the enzymes from whiteflies and the bacterium, Erwinia rhapontici, were compared. Partial purification of both enzymes showed that the enzyme from whiteflies was a 116 kD membrane-associated polypeptide, in contrast to the enzyme from E. rhapontici, which was soluble and 67 kD. The enzyme from E. rhapontici converted sucrose to isomaltulose and trehalulose in a 4:1 ratio, whereas the enzyme from whiteflies produced only trehalulose. Unlike the E. rhapontici enzyme, the whitefly enzyme did not convert isomaltulose to trehalulose, but both enzymes catalyzed the transfer of fructose to trehalulose using sucrose as the glucosyl donor. The results indicate that trehalulose synthase from whiteflies is structurally and functionally distinct from the sucrose isomerases described in bacteria. The whitefly enzyme is the first reported case of an enzyme that converts sucrose to exclusively trehalulose.