Cysteine-Rich Atrial Secretory Protein from the Snail Achatina achatina: Purification and Structural Characterization.

Sergey Shabelnikov,Artem Kiselev

doi:10.1371/journal.pone.0138787

Abstract

Despite extensive studies of cardiac bioactive peptides and their functions in molluscs, soluble proteins expressed in the heart and secreted into the circulation have not yet been reported. In this study, we describe an 18.1-kDa, cysteine-rich atrial secretory protein (CRASP) isolated from the terrestrial snail Achatina achatina that has no detectable sequence similarity to any known protein or nucleotide sequence. CRASP is an acidic, 158-residue, N-glycosylated protein composed of eight alpha-helical segments stabilized with five disulphide bonds. A combination of fold recognition algorithms and ab initio folding predicted that CRASP adopts an all-alpha, right-handed superhelical fold. CRASP is most strongly expressed in the atrium in secretory atrial granular cells, and substantial amounts of CRASP are released from the heart upon nerve stimulation. CRASP is detected in the haemolymph of intact animals at nanomolar concentrations. CRASP is the first secretory protein expressed in molluscan atrium to be reported. We propose that CRASP is an example of a taxonomically restricted gene that might be responsible for adaptations specific for terrestrial pulmonates.

Highlights

Gastropods are the largest and most diverse group of molluscs, with about 100,000 species inhabiting marine, freshwater and terrestrial habitats [1]
After a final reversed phase HPLC purification, we obtained virtually homogeneous samples of cysteine-rich atrial secretory protein (CRASP)-A (Fig 1C and 1E) and CRASP-B (Fig 1D and 1E), which were used for Edman degradation and mass spectrometry
We identified two CRASP isoforms, A and B, with CRASP-B differed by monoisotopic mass change of +0.97 Da and a pI shift of −0.07

Summary

Introduction

Gastropods are the largest and most diverse group of molluscs, with about 100,000 species inhabiting marine, freshwater and terrestrial habitats [1]. An interesting feature of the gastropod heart, are specialized secretory cells attached to the myocardial surface of the atrium. Until recently, they had only been described in Pulmonates: L. stagnalis [7], H. pomatia [8], H. aspersa, Strophocheilus oblongus [9], Achatina fulica [10] and Achatina achatina [11]. We called the ~16-kDa protein ‘cysteine-rich atrial secretory protein’ (CRASP) because it contains ten cysteine residues and its expression is highest in the atrium. This is the first report to describe the isolation and characterization of a secretory protein expressed in the atrium of gastropod molluscs

Results

Discussion

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