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Biochem Genet (2013) 51:413425
DOI 10.1007/s10528-013-9574-0
Hongwen Yang
Received: 10 June 2012 / Accepted: 21 September 2012 / Published online: 12 February 2013 Springer Science+Business Media New York 2013
Abstract L-gulono-gamma-lactone oxidase (GULO) catalyzes the nal step in vertebrate vitamin C biosynthesis. Vitamin C-incapable vertebrates lack the GULO gene. Gene structure and phylogenetic analyses showed that vertebrate GULO genes are 6495% identical at the amino acid level and consist of 11 conserved exons. GULO pseudogenes have multiple indel mutations and premature stop codons in higher primates, guinea pigs, and some bats. No GULO-like sequences were identied in teleost shes. During animal GULO evolution, exon F was subdivided into F1 and F2. Additional GULO retropseudogenes were identied in dogs, cats, and giant pandas. GULO-anking genome regions acquired frequent segment translocations and inversions during vertebrate evolution. Purifying selection was detected across vertebrate GULO genes (dN/dS = 0.069), except for some positively selected sites identied in sharks and frogs. These positive sites demonstrated little functional signicance when mapped onto the three-dimensional GULO protein structure. Vertebrate GULO genes are conserved except for those that are lost.
Keywords Vertebrates GULO loss Synteny analysis Selective pressure
Introduction
Vitamin C (L-ascorbic acid, AsA) is an indispensable, recycled reducing nutrient that acts as an antioxidant and is involved in animal collagen biosynthesis (Drouin
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H. Yang (&)
Biology Department, Zhangzhou Normal University, 36 Xian Qian Zhi Street, Zhangzhou 363000, Fujian, Chinae-mail: [email protected]
Conserved or Lost: Molecular Evolution of the Key Gene GULO in Vertebrate Vitamin C Biosynthesis
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et al. 2011). AsA is biosynthesized from glucose in animal livers or kidneys, with the terminal step being catalyzed by L-gulono-gamma-lactone oxidase (GULO, EC1.1.3.8). As an important antioxidant, AsA requirement and the correlated GULO activity often vary depending on different oxidative stress levels and are further correlated with varying energy requirements in animals. In addition, animal GULO activity also uctuates according to dietary AsA intake. For example, GULO activity in rabbits during the winter is higher than in the summer, indicating that less AsA is obtained from grass or that more energy is needed for rabbits in winter....