3BK3:
reference: Crystal structure analysis reveals how the Chordin family member crossveinless 2 blocks BMP-2 receptor binding., Zhang JL, Qiu LY, Kotzsch A, Weidauer S, Patterson L, Hammerschmidt M, Sebald W, Mueller TD, Dev Cell. 2008 May;14(5):739-50. PMID: 18477456

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