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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 the Cβ-Cα vector. This simple division of the CN sphere results in two strikingly different measures, HSE-up and HSE-down. HSE-up is defined as the number of Cα atoms in the upper half (containing the pseudo-Cβ atom) and analogously HSE-down is defined as the number of Cα atoms in 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 its calculation. The position of this pseudo-Cβ atom (pCβ) is derived from the positions of preceding Cα−1 and the following Cα+1. The Cα-pCβ vector is calculated by adding the Cα−1-Cα0 and Cα+1-Cα0 vectors. HSE is used in predicting discontinuous B-cell epitopes.〔.〕 Recently Song et al. have developed an online webserver termed HSEpred to predict half-sphere exposure from protein primary sequences.〔.〕 HSEpred server can achieve the correlation coefficients of 0.72 and 0.68 between the predicted and observed HSE-up and HSE-down measures, respectively, when evaluated on a well-prepared non-homologous protein structure dataset. Moreover, residue contact number (CN) can also be accurately predicted by HSEpred webserver using the summation of the predicted HSE-up and HSE-down values, which has further enlarged the application of this new solvent exposure measure. ==References== 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Half sphere exposure」の詳細全文を読む スポンサード リンク
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