HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ricci, M. S. Articles by Brems, D. N. Search for Related Content PubMed PubMed Citation Articles by Ricci, M. S. Articles by Brems, D. N. Social Bookmarking                   What's this?

pH Dependence of structural stability of interleukin-2 and granulocyte colony-stimulating factor

¹ Pharmaceutics Department, Amgen Inc., Thousand Oaks, California 91320, USA
² Department of Chemical Engineering and
³ Biological Engineering Division, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

Reprint requests to: Margaret Speed Ricci, Pharmaceutics Department, Amgen Inc., 1 Amgen Center Drive, Thousand Oaks, CA 91320, USA; e-mail: mspeed{at}amgen.com; fax: (805) 375-5794.

After a cytokine binds to its receptor on the cell surface (pH ~7), the complex is internalized into acidic endosomal compartments (pH ~5–6), where partially unfolded intermediates can form. The nature of these structural transitions was studied for wild-type interleukin-2 (IL-2) and wild-type granulocyte colony-stimulating factor (G-CSF). A noncoincidence of denaturation transitions in the secondary and tertiary structure of IL-2 and tertiary structural perturbations in G-CSF suggest the presence of an intermediate state for each, a common feature of this structural family of four-helical bundle proteins. Unexpectedly, both IL-2 and G-CSF display monotonic increases in stability as the pH is decreased from 7 to 4. We hypothesize that such cytokines with cell-based clearance mechanisms in vivo may have evolved to help stabilize endosomal complexes for sorting to lysosomal degradation. We show that mutants of both IL-2 and G-CSF have differential stabilities to their wild-type counterparts as a function of pH, and that these differences may explain the differences in ligand trafficking and depletion. Further understanding of the structural changes accompanying unfolding may help guide cytokine design with respect to ligand binding, endocytic trafficking, and, consequently, therapeutic efficacy.

Keywords: Protein folding; protein stability; equilibrium denaturation; folding intermediates; endocytic trafficking; IL-2; G-CSF

CiteULike    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?