Abstract
Bacteriophage T4 lysozyme (T4L) has been used as a paradigm for seminal biophysical studies on prote in structure, dynamics, and stability. Approximately 700 mutants of this proteinand their respective complexes have been characterized by X-ray crystallography; however,despite the high resolution diffraction limi ts attained in several studies, no hydrogen atoms were reported being visualized in the electron density maps. To address this, a 2.2 A˚-resolution neutron data set was collected at 80 K from a crystal of perdeuterated T4L pseudo-wild type. We describe a near complete atomic structure of T4L, which includes the positions of 1737 hydrogen atomsdetermined by neutron crystallography. The cryogenic neutron model reveals explicit detail of thehydrogen bonding interactions in the protein, in addition to the protonation states of several impor-tant residues.
