The crystal structure of a hypothetical protein MJ0366, derived from Methanocaldococcus jannaschii was solved at 1.9 angstrom resolution using synchrotron radiation. MJ0366 was crystallized as a monomer and has knot structural arrangement. Intriguingly, the solved structure consists of novel 'KNOT' fold conformation. The 31 trefoil knot was observed in the structure. The N-terminal and C-terminal ends did not participate in knot formation. (C) 2016 Elsevier Inc. All rights reserved.