Comparison of protein structural model of ABCC2Ser1342Tyr mutation
ABCC2 have consisted of 32 exons involved in bile formation which mediates hepatobiliary excretion of numerous organic anions and conjugated organic anions such as methotrexate and also transports sulfated bile salt such as taurolithocholate sulfate.20, 21 This gene has two main nucleotide binding domains which located at position 671-678 and 1334-1341 (Figure 2A), separately. This location of this variant (Ser1342Tyr) in this study is closely to the ATP binding functional domain (1334-1341).
To further investigate the possible effects of the missense variant on protein structure, the reference and the modified protein structure ofABCC2 gene were compared simultaneously using UCSF Chimera 1.14rc. The result showed that, compared reference molecular structure, the 3D model of mutation have a slight change in the chemical bond lengths of ATP-ligand binding amino acid side chains at positions Ser1342, Ser678 and Gln706 (Figure 2B). The change in the amino side chains could affect the binding efficiency of the ATP molecular.
To further analysis the genetic basis of ABCC2 , we analyzed the mRNA expression level of ABCC2 gene in placental tissue between 2 healthy and four ICP patients using the GEO datasets derived from NCBI (GEO accession: GSE46157), when having no liver targeted tissue. The significant (P < 0.05) difference in the gene expression was observed between the two groups (Figure 2C). And the expression of ABCC2 upregulated in ICP group. Besides, we also detected that the expression of other three genes, such as ABCC6 ,ABCE1 and ABCG5 , have changed in placental tissue (See Supplementary material, Figure S4).