Replacement of the antifreeze-like domain of human N-acetylneuraminic acid phosphate synthase with the mouse antifreeze-like domain impacts both N-acetylneuraminic acid 9-phosphate synthase and 2-keto-3-deoxy-D-glycero-Dgalacto- nonulosonic acid 9-phosphate synthase activities

Abstract

Human NeuNAc-9-P synthase is a two-domain protein with ability to synthesize both NeuNAc-9-P and KDN-9-P. Its mouse counterpart differs by only 20 out of 359 amino acids but does not produce KDN-9-P. By replacing the AFL domain of the human NeuNAc-9-P synthase which accommodates 12 of these differences, with the mouse AFL domain we examined its importance for the secondary KDN-9-P synthetic activity. The chimeric protein retained almost half of the ability of the human enzyme for KDN-9-P synthesis while the NeuNAc-9-P production was reduced to less than 10%. Data from the homology modeling and the effect of divalent ions and temperature on the enzyme activities suggest conformational differences between the human and mouse AFL domains that alter the shape of the cavity accommodating the substrates. Therefore, although the AFL domain itself does not define the ability of the human enzyme for KDN-9-P synthesis, it is important for both activities by aiding optimal positioning of the substrates.

Antifreeze protein gene amplification facilitated niche exploitation and speciation in wolffish

“…Wolffishes, and other members of the suborder Zoarcoidei, produce type III AFPs [26,28,37,45–47] that are generally believed to have evolved from the small C‐terminal domain of the enzyme sialic acid synthase [48,49] by a process of neofunctionalization [11,16], It is thought that there was a duplication of a gene encoding a sialic acid synthase that had both enzymatic and weak ice‐binding activity. At some point, the bulk of one duplicate was lost, leaving the ice‐active C‐terminal domain to evolve into a fully functional AFP [16].…”