Nucleotide and deduced amino acid sequence of bovine adrenal medulla chromogranin B (secretogranin I)

Dominant Expression of Chromogranin B in Pituitary Corticotrophs and Its Putative Role in Interaction With Secretogranin III

SummaryPrevious studies have suggested that chromogranin A (CgA) is a partner molecule of secretogranin III (SgIII). In mouse pituitary corticotroph-derived AtT-20 cells, SgIII plays a role in sorting CgA/hormone aggregates into secretory granules (SGs). Although CgA expression is equivocal, CgB is clearly detectable in the rat pituitary corticotrophs. Therefore, we hypothesized that CgB shares a function with CgA in pituitary corticotrophs. In the binding assays, CgB, similar to CgA, showed binding activity to SgIII under weakly acidic conditions and in the presence of Ca2+. Considering the differences in animal species, the different abilities of antibodies, and the conditions of tissue fixation and thin sectioning in immunofluorescence histochemistry, we found that CgA was expressed in a small population (approximately 10%), and its expression intensity was weaker than that of CgB (>98%) in rodent pituitary corticotrophs. In addition, similar to CgA, CgB and SgIII were colocalized in adrenocorticotropic hormone (ACTH) granules. The labeling of CgA and CgB was not completely consistent, and CgB colocalized with SgIII in many granules. These results suggest that there are multiple sorting systems for ACTH granules in pituitary corticotrophs and that the SgIII/CgB complex behaves more dominantly than the SgIII/CgA complex, which has somewhat different properties.

New insights into granin-derived peptides: evolution and endocrine roles

The granin protein family is composed of two chromogranin and five secretogranin members that are acidic, heat-stable proteins in secretory granules in cells of the nervous and endocrine systems. We report that there is little evidence for evolutionary relationships among the granins except for the chromogranin group. The main granin members, including chromogranin A and B, and secretogranin II are moderately conserved in the vertebrates. Several small bioactive peptides can be generated by proteolysis from those homologous domains existing within the granin precursors, reflecting the conservation of biological activities in different vertebrates. In this context, we focus on reviewing the distribution and function of the major granin-derived peptides, including vasostatin, bovine CgB(1-41) and secretoneurin in vertebrate endocrine systems, especially those associated with growth, glucose metabolism and reproduction.

Processing of chromogranin B in bovine adrenal medulla. Identification of secretolytin, the endogenous C-terminal fragment of residues 614-626 with antibacterial activity

Chromogranins constitute a family of acidic soluble proteins widely distributed in endocrine cells and neurons. Chromogranin A, the major soluble component in bovine adrenal medullary secretory granules in chromaffin cells, has been shown to be actively processed to peptide fragments [Metz-Boutigue, M. H., Garcia-Sablone, P., Hogue-Angeletti, R. & Aunis, D. (1993) Eur. J. Biochem. 217, 247-257]. In the present paper, the structural features of the proteolytic degradation mechanism of chromogranin B/secretogranin I have been characterized with regard to the possible function of this protein as a precursor of biologically active peptides. Chromogranin-B-derived fragments present in bovine chromaffin granules were identified by microsequencing after separation by two-dimensional gel electrophoresis or high-performance liquid chromatography. A similar approach was performed to characterize chromogranin-B-derived fragments released into the extracellular space from depolarized bovine cultured chromaffin cells. In chromogranin B, 18 cleavage sites were identified along the protein chain and chromogranin B/secretogranin I fragments were generated by proteolytic attack at both the N-terminus and C-terminus. A major fragment corresponding to residues 614-626 of the C-terminal sequence, was identified in the extracellular space; this peptide was found to share sequence and structural similarities with the lytic domain of cecropins and, as expected from this similarity, to display potent antibacterial properties. Endogenous and synthetic peptides were active on Micrococus luteus, killing bacteria in the micromolar concentration range. The synthetic peptide slows the growth of Bacillus megaterium and was inactive towards Escherichia coli. In addition, the synthetic peptide was unable to induce hemolytic activity. This antibacterial function might be of biological significance in the neuroendocrine system of living organisms. We propose to name this peptide secretolytin.

Posttranslational processing of proenkephalins and chromogranins/secretogranins

Posttranslational processing of peptide-precursors is nowadays believed to play an important role in the functioning of neurons and endocrine cells. Both proenkephalins and chromogranins/secretogranins are considered as precursor molecules in these tissues, resulting in posttranslationally formed degradation products with potential biological activities. Among the proteins and peptides of neuronal and endocrine secretory granules, the enkephalins and enkephalin-containing peptides have been most extensively studied. The characterization of the post-translationally formed degradation products of the proenkephalins have enabled the understanding of their processing pathway. Chromogranins/secretogranins represent a group of acidic glycoproteins, contained within hormone storage granules. The biochemistry, biogenesis and molecular properties of these proteins have already been studied for 25 years. The chromogranins/secretogranins have a widespread distribution throughout the neuroendocrine system, the adrenal medullary chromaffin granules being the major source of these storage components. Recent data provide evidence for a precursor role for all members of the chromogranins/secretogranins family although also several other functions have been proposed. In this review, some of the methods applied to study proteolytic processing are described. In addition, the posttranslational processing of chromogranins/secretogranins and proenkephalins, especially the biochemical aspects, will be discussed and compared. Recent exciting developments on the generation and identification of potential physiologically active fragments will be covered.