Dear all, I want to calculate frequency of various residues in transmembrane protein. For this, I have to align the membrane protein in the bilayer so that z-axis is parallel to bilayer normal. Then, i have to calculate frequency of any residue at a particular distance in Å from the centre of bilayer(z = 0). This seems to be normal practice for aligning transmembrane proteins after getting coordinates from PDB structure. Could someone please guide me as to how this can be done in python or Bio-python?