# Why are there no hydrogen atoms in the crystal structure of a biomolecule?

I am taking a physics and chemistry at the nanoscale class at my university and for a project I must learn how to use Visual Molecular Dynamics (VMD). One of the models involved in this project is apo-core-streptavidin in complex with biotin at pH 4.5 (1SWE.pdb). The crystal structure can be found protein data bank. There are no hydrogen atoms in this file/model and I was wondering why that is. I can't find the answer to this anywhere online.

• Welcome to Chemistry.SE! Take the tour to get familiar with this site. Mathematical expressions and equations can be formatted using $\LaTeX$ syntax. With X-ray crystallography you measure electron density, for light elements the uncertainty is probably too high to depict their position accurately. Have a look at this file, maybe it helps you a little until you receive an answer. – Martin - マーチン Mar 22 '16 at 5:17
• – andselisk Oct 9 '17 at 12:16