Stuctures of Heme and Hemozoin

Heme

Protoporphyrin IX

Heme is found in almost all organisms and functions in a variety of redox and other types of reactions. A well known function of heme is its role as an oxygen carrier in hemoglobin. The structure of heme consists of a large ring, called porphyrin, with an iron atom in the center (Figure). This particular type of heme is also known as protophorphyrin IX. The four nitrogens (N) of the porphyrin ring coordinate with the iron (Fe) to hold it in place. The iron can still interact with other ligands such as oxygen. Overall, heme has a flat and planar structure.

Digestion of hemoglobin by the malaria parasite results in the release of free heme. Some of this free heme will aggregate into large crystals known as hemozoin, or the malaria pigment. The basic unit of these crystals are b-hematin. b-hematin is formed from two heme molecules via reciprocal bonds (shown in purple) between carboxylic acids groups and the iron atoms.

beta-hematin

Ball and Stick Representation of b-Hematin

These b-hematin dimers then interact via hydrogen-bonds to form a large crystal. Below is a space-filling model of the proposed structure of hemozoin. A single b-hematin unit is outlined in yellow.

Structure of Hemozoin

Figure modified from Pagola et al (2000, Nature 404:307). Colors are the same in all three figures (C = grey; O = red; N = green; Fe = blue). Lighter shades are closer to the viewer.


These pages are developed and maintained by Mark F. Wiser, Tulane University (ã2002). Last update 07/18/02.