Half sphere exposure

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.

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.

[2] Song et al. have developed an online webserver termed HSEpred to predict half-sphere exposure from protein primary sequences.

[3] 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.

Recently, Heffernan et al. has developed the most accurate predictor for both HSEα and HSEβ based on a big dataset by using multiple-step iterative deep neural-network learning.

Half Sphere Exposure (HSE) construction. This simple, two-dimensional measure of solvent exposure counts the number of neighbors in two domes (with radius R typically equal to 10 or 12 Å ) around the Cα atom. It is simple and extremely fast to compute, and superior to the widely used Contact Number measure. The HSE value pair (up and down) of the example above is (3,5).