The effect of amphiphilic additives on the growth and morphology of Aspergillus niger acid proteinase A crystals

The effect of amphiphilic additives, dimethyl sulfoxide (DMSO) and alkane d iols (HO(CH2)(n)OH, n = 2-6), on the crystallization of Aspergillus niger a cid proteinase A was investigated by optical and confocal laser microscopy. As DMSO concentration was increased, while keeping ammonium sulfate concen tration constant, the crystal clusters became larger and their number decre ased. The crystal cluster morphology changed from thin needles to rod-like. The amphiphilic nature of DMSO molecules seemed to suppress unfavorable hy drophobic interaction between protein molecules in the solution and in the crystal. To control the amphiphilic nature of additives, an alkane diol ser ies of n = 2-6 was examined in addition to DMSO. Single crystals were obtai ned at n = 4 and 5, while only crystal clusters were obtained at n = 2 and 3 and no crystals appeared at n = 6. These results suggest that the balance of hydrophobicity and hydrophilicity of additives is important in protein crystallization. (C) 2002 Elsevier Science B.V. All rights reserved.