Time evolution of crystallization phase of lysozyme protein in aqueous salt solution as studied by scattering techniques

Formation of protein crystallization in 1 wt% lysozyme in aqueous solution has been studied as a function of salt (KBr) concentration. The onset and the rate of crystallization in this protein solution strongly depend on the KBr concentration. It is found, while the presence of 0.4 M KBr starts producing crystals in 1 h, it takes about 120 h for 0.2 M KBr. The rate of protein crystallization has been studied by small-angle neutron scattering (SANS) and dynamic light scattering (DLS) in 1 wt% lysozyme solution in presence of three different KBr concentrations 0.3, 0.26 and 0.24 M, which show the start of crystallization at about 1.5, 3 and 5 h, respectively. Measurements have been performed for every half an hour from freshly prepared protein sample up to 72 h. Both time-evolved SANS and DLS data have been used to calculate the fraction of crystallization as a function of time. The variation of crystallization with time shows three distinguished regions: (i) prior to and the beginning of crystallization, which shows no significant change in the crystallization, (ii) growth region showing a significant increase in the crystallization with time and (iii) saturation region. These three regions have been found to be strongly depending on the start of the crystallization as controlled by the salt concentration.