Back to Search
Start Over
Contribution of Residue B5 to the Folding and Function of Insulin and IGF-l: CONSTRAINTS AND FINE-TUNING IN THE EVOLUTION OF A PROTEIN FAMILY.
- Source :
-
Journal of Biological Chemistry . 2/12/2010, Vol. 285 Issue 7, p5040-5055. 16p. - Publication Year :
- 2010
-
Abstract
- Proinsulin exhibits a single structure, whereas insulin-like growth factors refold as two disulfide isomers in equilibrium. Native insulin-related growth factor (IGF)-I has canonical cystines (A6-A11, A7-B7, and A20-B19) maintained by IGF-binding proteins; IGF-swap has alternative pairing (A7-A11, A6 -B7, and A20 -B19) and impaired activity. Studies of mini- domain models suggest that residue B5 (His in insulin and Thr in IGFs) governs the ambiguity or uniqueness of disulfide pairing. Residue B5, a site of mutation in proinsulin causing neonatal diabetes, is thus of broad biophysical interest. Here, we characterize reciprocal B5 substitutions in the two proteins. In insulin, HisB5 → Thr markedly destabilizes the hormone (ΔΔGu 2.0 ± 0.2 kcal/mol), impairs chain combination, and blocks cellular secretion of proinsulin. The reciprocal IGF-I substitution ThrB5 → His (residue 4) specifies a unique structure with native ¹H NMR signature. Chemical shifts and nuclear Overhauser effects are similar to those of native IGF-I. Whereas wild-type IGF-I undergoes thiol-catalyzed disulfide exchange to yield IGF-swap, HisB5-IGF-I retains canonical pairing. Chemical denaturation studies indicate that HisB5 does not significantly enhance thermodynamic stability (ΔΔGu 0.2 ± 0.2 kcal/mol), implying that the substitution favors canonical pairing by destabilizing competing folds. Whereas the activity of ThrB5-insulin is decreased 5-fold, HisB5-IGF-I exhibits 2-fold increased affinity for the IGF receptor and augmented post-receptor signaling. We propose that conservation of ThrB5 in IGF-I, rescued from structural ambiguity by IGF-binding proteins, reflects fine-tuning of signal transduction. In contrast, the conservation of HisB5 in insulin highlights its critical role in insulin biosynthesis. [ABSTRACT FROM AUTHOR]
- Subjects :
- *INSULIN
*CARRIER proteins
*GROWTH factors
*ISOMERASES
*CYSTINOSIS
*BIOSYNTHESIS
Subjects
Details
- Language :
- English
- ISSN :
- 00219258
- Volume :
- 285
- Issue :
- 7
- Database :
- Academic Search Index
- Journal :
- Journal of Biological Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 48847197
- Full Text :
- https://doi.org/10.1074/jbc.M109.062992