Half Sphere Exposure (HSE) is a protein solvent exposure measure that was first introduced by .Like all solvent exposure measures it measures how buried amino acid residues are in a protein. It is found by counting the number of amino acid neighbors within two half spheres of chosen radius around the amino acid. The calculation of HSE is found by dividing a contact number (CN) sphere in two halves by the plane perpendicular to theCβ-Cα vector. This simple division of the CN sphere results intwo strikingly different measures, HSE-up and HSE-down. HSE-up is defined as the number of Cα atoms in theupper half (containing the pseudo-Cβ atom) and analogously HSE-down is defined as the number of Cα atomsin the opposite sphere.
If only Cα atoms are available (as is the case for many simplified representations of protein structure), a related measure, called HSEα, can be used. HSEα uses a pseudo-Cβ instead of the real Cβ atom for itscalculation. The position of this pseudo-Cβ atom (pCβ) is derived from the positions of precedingCα<sup>−1</sup> and the following Cα<sup>+1</sup>. The Cα-pCβ vector is calculated by adding theCα<sup>−1</sup>-Cα<sup>0</sup> and Cα<sup>+1</sup>-Cα<sup>0</sup> vectors.
HSE is used in predicting discontinuous B-cell epitopes. Recently Song et al. have developed an online webserver termed HSEpred to predict... Read More