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We describe a straightforward crystallogenesis protocol leading to the preparation of protein crystals suitable for structure determination that involves protein expression and purification, refolding of the overexpressed protein, search of optimal crystallization conditions and diffraction data collection on native and selenomethionine substituted crystals. The protocol is exemplified with epididymal-specific lipocalin (rLcn6), a newly discovered monomeric protein of 19 kDa that may play an important role in sperm maturation. This protein was cloned from Norway rat (Rattus norvegicus) genome and expressed as insoluble inclusion bodies in Escherichia coli. After refolding of the purified protein, microcrystals were obtained after sparse matrix screening. Optimization of conditions after stepwise incremental initial conditions led to single crystals belonging to space group P212121 and data set at 1.90 A. After attempts with several models, initial phasing was not found by molecular replacement. A similar ...