Quinoline Binding Site on Malaria Pigment Crystal: A Rational Pathway for Antimalaria Drug Design

Human malaria, one of the most striking, reemerging infectious diseases, is caused by several types of Plasmodium parasites. As the parasite digests hemoglobin in human red blood cells, the heme byproduct crystallizes into micron-sized malaria-pigment (hemozoin). Making use of a recently reported powder-crystal structure determination of synthetic hemozoin (β-hematin), we describe here its theoretical growth form and show it to be similar in habit and form to that of natural hemozoin. With this information, we propose a noncovalent binding site for the quinoline drug family at the end face of the fastest-growing direction of β-hematin. This adsorption mechanism is examined in terms of crystal growth inhibition vis-à-vis published data. The surface binding site elucidates the difference in activity of various quinolines, revealing the importance of the different quinoline functionalities. The interplay between molecular chirality of quinolines and the chirality of centrosymmetric β-hematin crystal faces is analyzed in terms of crystal growth inhibition. We additionally propose a molecular isomerism of the crystalline building blocks, with implications on quinoline surface binding, as well as on nucleation and size of β-hematin crystals.