Journal of Biological Chemistry
Volume 278, Issue 50, 12 December 2003, Pages 50810-50817
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Mechanisms of Signal Transduction
Role of Disulfide Bonds in Acrp30/Adiponectin Structure and Signaling Specificity: DIFFERENT OLIGOMERS ACTIVATE DIFFERENT SIGNAL TRANSDUCTION PATHWAYS*

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Acrp30/adiponectin is an adipocyte-derived serum protein with important roles in regulation of lipid and glucose metabolism, but which of its isoforms are biologically active remains controversial. We addressed this issue by first characterizing the structure of each individual Acrp30 oligomer and the determinants responsible for multimer formation. Freeze etch electron microscopy showed the trimer to exhibit a ball-and- stick-like structure containing a large globular sphere, an extended collagen stalk, and a smaller sphere on the opposite end of the stalk. The hexamer consists of two adjacent trimeric globular domains and a single stalk composed of collagen domains from two trimers. Although not necessary for trimer formation or stability, two of the three monomers in an Acrp30 trimer are covalently linked by a disulfide bond between cysteine residues at position 22. In contrast, assembly of hexameric and higher molecular weight (HMW) forms of Acrp30 depends upon formation of Cys22-mediated disulfide bonds because their reduction with dithiothreitol or substitution of Cys22 with alanine led exclusively to trimers. HMW and hexamer isoforms of Acrp30 activated NF-κB in C2C12 cells, but trimers, either natural, formed by reduction of Acrp30 hexamer, or formed by the C22A mutant, did not. In contrast, incubation of isolated rat extensor digitorum longus with naturally formed Acrp30 trimers or trimeric C22A Acrp30 led to increased phosphorylation of AMP-activated protein kinase-α at Thr172 and its activation. Hexameric and HMW Acrp30 could not activate AMP-activated protein kinase. Thus, trimeric and HMW/hexameric Acrp30 activate different signal transduction pathways, and Acrp30 represents a novel example of the control of ligand signaling via changes in its oligomerization state.

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Supported in part by National Institutes of Health Grant R37DK47618 and by a grant from Genset Corporation.

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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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Supported by fellowships from the Ares-Serono Foundation and the American Diabetes Association.