Factors that distort the heme structure in Heme-Nitric Oxide/OXygen-Binding (H-NOX) protein domains. A theoretical study

► The natural tendency of the heme is to be planar. ► Several factors are responsible for the strong structural distortion in H-NOX. ► The polar residues play major roles in distorting the heme structure. ► The dispersion correction greatly improves the calculated structures. ► The different heme conformations in H-NOX and Mb are reproduced by the calculation.