There are manifest scientific and technological interests in organizing nanocrystals (NC) into controlled architectures and work is rapidly expanding in exploiting opportunities through bio-assembly processes. In this research, we have applied biologically assembled nano-scale template to direct formation of precisely defined 2D nanocrystal arrays. We explored purple membrane (PM), a naturally occurring membrane protein (bacteriorhodopsin, BR) crystal patch from halobacteria, as a precisely structured nanometer-scale template. We have developed genetically engineered PMs that display unique functional group (cystein) on the membrane surfaces with precisely defined nano-scale symmetry. These reactive functional groups were used as specific anchoring sites for NC immobilization. We show that the cystein mutants of BR mutated at the surface of the PM are capable of forming stable PM-like hexagonal crystal lattices in the host cell membrane. These crystal patches are easily purified by ultracentrifugation and can be used to react with functionallized gold nanoclusters. We also present the variation of crystal lattice by detergent treatment and recrystallization techniques. The PM has been known to posses good materials properties and is expected to allow formation of robust nanocrystal array that can withstand variety of optical and electrical characterization conditions.