Microsomal triglyceride transfer protein (MTP) is essential in lipid metabolism, especially in the biogenesis of very low-density lipoproteins and chylomicrons via the transfer of neutral lipids and the assembly of apoB-containing lipoproteins. It is a heterodimer consisting of a large MTP alpha-subunit and a protein disulfide isomerase (PDI) beta-subunit. The MTP large subunit has and N-terminal beta-barrel domain, a central alpha-helical domain and a C-terminal 2-beta-sheet domain. This is the highly conserved MTP C-terminal domain involved in lipid-binding and transfer activity, with preference of neutral 3 chain-containing lipids. The beta-sheets are named A and C and form a sandwich comprising the lipid-binding site between them. Half of the A-sheet interacts with the beta-barrel. This domain also interacts with a' and b' domains of PDI [1].

1: The crystal structure of human microsomal triglyceride transfer protein. Biterova EI, Isupov MN, Keegan RM, Lebedev AA, Sohail AA, Liaqat I, Alanen HI, Ruddock LW; Proc Natl Acad Sci U S A. 2019;116:17251-17260. PMID:31395737