Nucleoplasmin histone-chaperone protein, molecular model. This is nucleoplasmin 2 (Npm2), a chaperone that acts on human nucleoplasmin. Chaparone proteins play a key role in aiding protein folding. This one binds to histone, the proteins around which DNA (deoxyribonucleic acid) is packaged in cell nuclei. Nucleoplasmin 2 occurs in humans in oocytes (female reproductive cells) and embryos. This structure is a decamer (ten-fold structure) consisting of two pentamers. The protein chains, forming a ring, are indicated by the colours.