6B4M

Structural characterization of a novel monotreme-specific protein from the milk of the platypus

Summary for 6B4M

• Entry DOI: 10.2210/pdb6b4m/pdb
• Related: 4v00 4v3j
• Descriptor: Monotreme lactation protein, 2-acetamido-2-deoxy-beta-D-glucopyranose, IODIDE ION, ... (5 entities in total)
• Functional Keywords: monotreme, novel-fold, antimicrobial protein
• Biological source: Ornithorhynchus anatinus (Duckbill platypus)
• Total number of polymer chains: 2
• Total formula weight: 83125.72

Authors

Peat, T.S.,Newman, J.,Sharp, J.A.,Kumar, A.,Nicholas, K.R.,Adams, T.E. (deposition date: 2017-09-27, release date: 2018-01-17, Last modification date: 2024-10-23)

Primary citation

Newman, J.,Sharp, J.A.,Enjapoori, A.K.,Bentley, J.,Nicholas, K.R.,Adams, T.E.,Peat, T.S.
Structural characterization of a novel monotreme-specific protein with antimicrobial activity from the milk of the platypus.
Acta Crystallogr F Struct Biol Commun, 74:39-45, 2018

PubMed Abstract: Monotreme lactation protein (MLP) is a recently identified protein with antimicrobial activity. It is present in the milk of monotremes and is unique to this lineage. To characterize MLP and to gain insight into the potential role of this protein in the evolution of lactation, the crystal structure of duck-billed platypus (Ornithorhynchus anatinus) MLP was determined at 1.82 Å resolution. This is the first structure to be reported for this novel, mammalian antibacterial protein. MLP was expressed as a FLAG epitope-tagged protein in mammalian cells and crystallized readily, with at least three space groups being observed (P1, C2 and P2). A 1.82 Å resolution native data set was collected from a crystal in space group P1, with unit-cell parameters a = 51.2, b = 59.7, c = 63.1 Å, α = 80.15, β = 82.98, γ = 89.27°. The structure was solved by SAD phasing using a protein crystal derivatized with mercury in space group C2, with unit-cell parameters a = 92.7, b = 73.2, c = 56.5 Å, β = 90.28°. MLP comprises a monomer of 12 helices and two short β-strands, with much of the N-terminus composed of loop regions. The crystal structure of MLP reveals no three-dimensional similarity to any known structures and reveals a heretofore unseen fold, supporting the idea that monotremes may be a rich source for the identification of novel proteins. It is hypothesized that MLP in monotreme milk has evolved to specifically support the unusual lactation strategy of this lineage and may have played a central role in the evolution of these mammals.

PubMed: 29372906
DOI: 10.1107/S2053230X17017708

Experimental method

X-RAY DIFFRACTION (2.5 Å)