[NMR paper] Solution NMR Structure and Backbone Dynamics of the Partially Disordered Arabidopsis thaliana Phloem Protein 16-1, A Putative mRNA Transporter.

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Solution NMR Structure and Backbone Dynamics of the Partially Disordered Arabidopsis thaliana Phloem Protein 16-1, A Putative mRNA Transporter.

Solution NMR Structure and Backbone Dynamics of the Partially Disordered Arabidopsis thaliana Phloem Protein 16-1, A Putative mRNA Transporter.

Biochemistry. 2018 Jan 10;:

Authors: Sashi P, Singarapu KK, Bhuyan AK

Abstract
Although RNA-binding proteins in plant phloem are believed to carry out long-distance systemic transport of RNA in the phloem conduit, the structure of none of them is known. The Arabidopsis thaliana phloem protein 16-1 (AtPP16-1) is such a putative mRNA transporter whose structure and backbone dynamics have been studied at pH 4.1, 25oC, by high-resolution NMR spectroscopy. Results obtained using basic optical spectroscopic tools show that the protein is unstable with little secondary structure near the physiological pH of the phloem sap. Fluorescence-monitored titrations reveal that AtPP16-1 binds not only A. thaliana RNA (Kdiss ~ 67 nM) but also sheared DNA and model dodecamer DNA, albeit the affinity for DNA is ~15-fold less. In the solution structure of the protein secondary structural elements are formed of residues 3-9 (?1), 56-62 (?2), 133-135 (?3), and 96-110 (??-helix). Most of the rest of the chain segments is disordered. The N-terminal disordered regions (residues 10-55) form a small lobe, which conjoins the rest of the molecule via a deep and large irregular cleft that could have functional implications. The average order parameter extracted by model-free analysis of 15N relaxation and {1H}-15N heteronuclear NOE data is 0.66, suggesting less restricted backbone motion. The average conformational entropy of the backbone NH vectors is -0.31 cal mol-1 K-1. These results also suggest structural disorder in AtPP16-1.


PMID: 29320165 [PubMed - as supplied by publisher]



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