MD SIMULATIONS OF THE TRANSMEMBRANE REGION OF GOLGI GLYCOSYLTRANSFERASES

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The beta-1,4-galactosyltransferase (beta-1,4GT) is a Golgi resident type II integral membrane protein, with a short cytoplasmic N-terminal domain, a transmembrane domain (TMD) and a large luminal C-terminal domain which is involved in the terminal glycosylation of secreted proteins. The TMD in this and in other similar Golgi resident proteins is largely hydrophobic in character and on the average shorter than the corresponding TMD in the plasma membrane type II proteins, and has been shown to be important for Golgi retention. However, the exact mechanism of its Golgi retention still remains unknown. The molecular dynamics (MD) simulation of the TMD of beta-1,4GT has been conducted to investigate whether its dynamic structural variations play any role in its Golgi retention. The starting structure of the TMD was assumed to be alpha-helical and the simulations were conducted in a periodic box of octonal molecules to account for the low dielectric membrane medium. Simulation of a double mutant in the TMD of beta-1,4GT (His->Leu, Cys->Ser), which shows lack of Golgi retention, was also conducted. Preliminary results show that the TMD of the wild type and double mutant have very similar dynamic behavior. A detailed MD simulations will aid in the understanding of the structural variations in TMD and the role it plays in Golgi retention.