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![P-glycoprotein (ABCB1) - weak dipolar interactions provide the key to understanding allocrite recognition, binding, and transport](https://image.oaes.cc/ff7a1ada-98b3-407e-90ab-aa6a690d0dac/5304.fig.1.jpg)
Figure 1. Examples of allocrites. Allocrites for ABCB1 are amphiphilic (polar part in blue, hydrophobic part in yellow) and carry type I or type II π-electron donor patterns (i.e., hydrogen bond acceptor patterns, HBAs) that are attracted by the HBDs in the protein. A type I pattern contains two HBAs separated by 2.5 ± 0.3 Å and a type II pattern contains two or three HBAs, where the outer two are separated by 4.5 ± 0.6 Å. Possible type I and type II patterns are encircled in blue: (A) Colchicine, two type II patterns. (B) Gemcitabine is an anticancer drug, which induces cell death by blocking DNA replication, with either two type I patterns (shown) or one type II pattern (not shown). (C) Tetramethylrosamine (TMR), type II patterns. (D) Rhodamine 6G (R6G), one type I pattern (secondary and primary amino groups are not involved in patterns). (E) Auraptene, a citrus phytochemical, one type I or one type II pattern. The orientation of the π-electrons in a pattern does not seem crucial. Unsaturated rings play a role in π-π stacking interactions.