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Human Neuromodulator SLURP-1: Bacterial Expression, Binding to Muscle-Type Nicotinic Acetylcholine Receptor, Secondary Structure, and Conformational Heterogeneity in Solution

M. A. Shulepko1,2, E. N. Lyukmanova1*, A. S. Paramonov1, A. A. Lobas1, Z. O. Shenkarev1, I. E. Kasheverov1, D. A. Dolgikh1,2, V. I. Tsetlin1, A. S. Arseniev1, and M. P. Kirpichnikov1,2

1Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, ul. Miklukho-Maklaya 16/10, 117997 Moscow, Russia; fax: (495) 330-6983; E-mail: ekaterina-lyukmanova@yandex.ru

2Biological Faculty, Lomonosov Moscow State University, 119991 Moscow, Russia

* To whom correspondence should be addressed.

Received September 3, 2012; Revision received October 22, 2012
Human protein SLURP-1 is an endogenous neuromodulator belonging to the Ly-6/uPAR family and acting on nicotinic acetylcholine receptors. In the present work, the gene of SLURP-1 was expressed in E. coli. The bacterial systems engineered for SLURP-1 expression as fused with thioredoxin and secretion with leader peptide STII failed in the production of milligram quantities of the protein. The SLURP-1 was produced with high-yield in the form of inclusion bodies, and different methods of the protein refolding were tested. Milligram quantities of recombinant SLURP-1 and its 15N-labeled analog were obtained. The recombinant SLURP-1 competed with 125I-α-bungarotoxin for binding to muscle-type Torpedo californica nAChR at micromolar concentrations, indicating a partial overlap in the binding sites for SLURP-1 and α-neurotoxins on the receptor surface. NMR study revealed conformational heterogeneity of SLURP-1 in aqueous solution, which was associated with cis-trans isomerization of the Tyr39–Pro40 peptide bond. The two structural forms of the protein have almost equal population in aqueous solution, and exchange process between them takes place with characteristic time of about 4 ms. Almost complete 1H and 15N resonance assignment was obtained for both structural forms of SLURP-1. The secondary structure of SLURP-1 involves two antiparallel β-sheets formed from five β-strands and closely resembles those of three-finger snake neurotoxins.
KEY WORDS: nicotinic acetylcholine receptor, bacterial expression, Lynx, conformational exchange, three-finger snake neurotoxin, NMR spectroscopy

DOI: 10.1134/S0006297913020090