Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 2000
Publication Date: N/A
Interpretive Summary: Adrenomedullin is a relatively small peptide hormone that has a variety of physiological capabilities including regulation of blood pressure, regulation of sugar metabolism, and some properties to act as a natural antimicrobial peptide. Our laboratories were the first to discover that adrenomedullin is in part transported in blood bound to a transport binding gprotein. In the present studies we have used traditional protein sequencing technologies to determine the structure of this binding protein and have matched it to a member of the complement system called complement factor-H. Our data show that the binding protein modifies the functions of adrenomedullin, selectively increasing the biological effects and in other situations decreasing the effects of adrenomedullin. In addition, we have shown that the binding of adrenomedullin to factor H increases the ability for factor H to process another important factor, C3B. The impact of this research is that it is the first data to demonstrate how adrenomedullin ca have multiple functions at multiple sites in the body. The binding protein imparts differences in function to the adrenomedullin. This should prove interesting in understanding why certain diseases states, like some forms of diabetes, that have an adrenomedullin component to the disease vary in the degree of host response.
Adrenomedullin (AM) is an important regulatory peptide involved in both physiological and pathophysiological states. We have previously demonstrated the existence of a specific AM binding protein (AMBP-1) in human plasma. In the present study we developed a non-radioactive ligand blotting which, together with HPLC/SDS-PAGE purification techniques allowed dus to isolate AMBP-1 to homogeneity. The purified protein was subjected t total amino acid sequencing, N-terminal sequence, and a mass spectrometry. The results identified AMBP-1 as human complement factor-H. We show that AM/Factor H interaction interferes with the established methodology for quantification of circulating AM. Our data suggests that this routine procedure does not take into account the AM bound to the binding protein. In addition, we show that factor-H has diametric effects on AM in vitro functions. It enhances AM-mediated induction of camp in fibroblasts but suppresses the bactericidal capability of AM on E. coli. Reciprocally, AM influences the complement regulatory function of factor-H by enhancing the cleavage of C3B via factor I. In summary, we report on a newly identified regulatory mechanism of AM biology, the influence of factor-H on radioimmunoassay quantification of AM, and the possible involvement of AM as a regulator of the complement cascade.