Isolation and primary structure of the three major forms of granulin-like peptides from hematopoietic tissues of a teleost fish (Cyprinus carpio).

Granulins are cysteine-rich polypeptides purified from human and rat hematopoietic cells and structurally related to the epithelin family of growth modulatory factors. A prototypic form of granulin was isolated from the hematopoietic organs of teleost fish (Belcourt, D., and Bennett, H.P.J. (1988) J. Cell Biol. 107, 629 (abstr.)). This study reports the structure of three granulins purified from the spleen and head kidney of the carp (Cyprinus carpio). Ion-spray mass spectrometric analysis of granulin-1, -2, and -3 corroborated the observed primary structures and demonstrated that each 57-residue-peptide was monomeric in nature with all cysteines linked via intramolecular disulfide bridges. A comparison of the carp granulin sequences demonstrates that granulins 2 and 3 are most closely related with sequence variations occurring primarily toward the amino terminus. A rabbit polyclonal antibody was raised against carp granulin-1 to develop a radioimmunoassay for this peptide, which showed no significant cross-reactivity with granulin-2 and -3. The distribution of carp granulin-1 was studied by screening purified tissue extracts for immunoreactivity using reversed-phase high performance liquid chromatography. A single form of immunoreactive granulin-1 was identified in all carp tissues studied including spleen, head kidney, heart, skin, gills, and gut. These studies have established that members of the granulin/epithelin family are found in a lower vertebrate and may serve important growth modulatory functions throughout the vertebrate kingdom.