3ENT:
reference: Three-dimensional domain swapping in nitrollin, a single-domain betagamma-crystallin from Nitrosospira multiformis, controls protein conformation and stability but not dimerization., Aravind P, Suman SK, Mishra A, Sharma Y, Sankaranarayanan R, J Mol Biol. 2009 Jan 9;385(1):163-77. Epub 2008 Oct 19. PMID: 18976659

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