Mutations in intracellular loop 3 affect the proper packing of human P-glycoprotein and lead to misfolding of this ABC transporter

Wednesday, November 06, 2013 — Poster Session I
4:00 p.m. – 6:00 p.m.	FAES Academic Center (Upper-Level Terrace)	NCI	MOLBIO-12

Authors

K Kapoor
J Bhatnagar
E Chufan
S.V. Ambudkar

Abstract

P-glycoprotein (ABCB1) is an ATP-Binding Cassette (ABC) transporter that effluxes anticancer drugs out of the cell. Homology model of human P-gp based on crystal structure of C. elegans P-gp suggests that residues in ICL1 (D164) and ICL3 (D805) interact with NBDs via ball-and-socket joint thus creating a more extensive network surface between TMDs and NBDs (Jin et. al., 2012). It was observed that D164C/D805C mutant when expressed in HeLa cells led to misprocessing of P-gp and failed to transport all tested drug substrates. The misprocessed protein is trapped intracellularly and associates more with chaperone Hsp70.This misfolded protein could be rescued to cell surface by growing at lower temperature (27°C), treatment with substrates (cyclosporine A), modulators (tariquidar) or small corrector molecules for 4-18 hrs. The homology model of human P-gp based on crystal structure of mouse P-gp shows SNPs D800N, V801M and D1088N are located spatially close to Asp805 and all these residues together result in a tight cluster. It was observed that mutation D800A when expressed in HeLa cells also resulted in misprocessing of this protein. Taken together, these data suggest that the residues in this region (ICL3) of the protein play a crucial role in proper folding of P-gp.