Structural analysis in nonsymbiotic hemoglobins: what can we learn from inner cavities?

TitleStructural analysis in nonsymbiotic hemoglobins: what can we learn from inner cavities?
Publication TypeJournal Article
Year of Publication2011
AuthorsSpyrakis, F, Luque FJ, Viappiani C
JournalPlant science : an international journal of experimental plant biology
Pagination8 - 13
Date Published2011/07//
KeywordsArabidopsis Proteins/chemistry; Crystallography, Plant; Hemoglobins/chemistry; Hydrophobic and Hydrophilic Interactions; Nitric Oxide/metabolism; Oxygenases/chemistry; Plant Proteins/chemistry; Protein Structure, Tertiary, X-Ray; Gene Expression Regulation
AbstractPlants contain three classes of hemoglobins which are not associated with nitrogen fixing bacteria, and have been accordingly termed nonsymbiotic hemoglobins. The function of nonsymbiotic hemoglobins is as yet mostly unknown. A NO dioxygenase activity has been proposed and demonstrated for some of them in vitro. In this context, a sound molecular mechanism that relates the structure with the biological activity is crucial to suggest a given physiological role. Insight into such a mechanism is now facilitated by recent progress made in both experimental and computational techniques. These studies have highlighted a number of key structural features implicated in the function of nonsymbiotic hemoglobins. The bis-histidyl hexacoordination of the heme in both its ferric and ferrous states provides a powerful and general tool to modulate reactivity, protein dynamics, and shape of the cavities. In addition, the specific arrangement of distal cavity residues provides effective protection against autoxidation. Inspection of the static crystal structures available for both liganded and unliganded states seems unsufficient to explain the function of these proteins. Function appears to be intimately linked with protein flexibility, which influences the dynamical behavior of inner cavities, capable of delivering apolar reactants to the reaction site, and removing charged reaction products. In this mini review, we demonstrate how the integration of information derived from experimental assays and computational studies is valuable and can shed light into the linkage between structural plasticity of nonsymbiotic hemoglobins and their biological role.