National Center for
4JP7: High Resolution Structure Of A Papaya Barwin-like Protein (crystal Form 2)
High-resolution structure of a papaya plant-defence barwin-like protein solved by in-house sulfur-SAD phasing
Acta Crystallogr. D Biol. Crystallogr. (2013) 69 p.2017-2026
The first crystal structure of a barwin-like protein, named carwin, has been determined at high resolution by single-wavelength anomalous diffraction (SAD) phasing using the six intrinsic S atoms present in the protein. The barwin-like protein was purified from Carica papaya latex and crystallized in the orthorhombic space group P212121. Using in-house Cu Kalpha X-ray radiation, 16 cumulative diffraction data sets were acquired to increase the signal-to-noise level and thereby the anomalous scattering signal. A sequence-database search on the papaya genome identified two carwin isoforms of 122 residues in length, both containing six S atoms that yield an estimated Bijvoet ratio of 0.93% at 1.54 A wavelength. A systematic analysis of data quality and redundancy was performed to assess the capacity to locate the S atoms and to phase the data. It was observed that the crystal decay was low during data collection and that successful S-SAD phasing could be obtained with a relatively low data multiplicity of about 7. Using a synchrotron source, high-resolution data (1 A) were collected from two different crystal forms of the papaya latex carwin. The refined structures showed a central beta-barrel of six strands surrounded by several alpha-helices and loops. The beta-barrel of carwin appears to be a common structural module that is shared within several other unrelated proteins. Finally, the possible biological function of the protein is discussed.