Probing the stability of a partly folded apomyoglobin intermediate by site-directed mutagenesis.


A partly folded form (I) of apomyoglobin has an alpha-helix content of about 35%; in an earlier study, hydrogen exchange revealed that the A, G, and H helices are folded, while much of the rest of the protein is not [Hughson, F. M., Wright, P. E., & Baldwin, R. L. (1990) Science 249, 1544-1548]. Because A, G, and H form a compact subdomain in native myoglobin, we proposed that nativelike packing interactions among the three helices might be retained in the I form of apomyoglobin. To test this proposal, disruptive mutations were introduced into the A.H and G.H helix packing sites. These mutations destabilize native apomyoglobin relative to I. In contrast, the stability of I is relatively insensitive to mutation; in particular, side-chain volume alone does not appear to be important. These results indicate that the I form is not stabilized by nativelike A.H and G.H packing interactions. In support of this we show that partly helical peptides derived from the G and H helix regions of myoglobin do not pair in solution. Since the isolated G and H peptides are at best only partly helical, some type of interaction must stabilize these helices in the I form. Small increases in the stability of I are seen when mutation introduces a side chain of increased nonpolar surface area. We suggest that I is stabilized by relatively nonspecific hydrophobic interactions that allow it to adapt easily to mutation. In this and other respects, I appears to conform to the "molten globule" model, with the caveat that only part of the polypeptide chain appears to participate in the globule. Study holds ProTherm entries: 328, 329, 330, 331 Extra Details: apomyoglobin; site-directed mutagenesis; alpha-helix;,hydrophobic interactions; molten globule; stability

Submission Details


Submitter: Connie Wang

Submission Date: April 24, 2018, 8:15 p.m.

Version: 1

Publication Details
Hughson FM;Barrick D;Baldwin RL,Biochemistry (1991) Probing the stability of a partly folded apomyoglobin intermediate by site-directed mutagenesis. PMID:2021603
Additional Information

Structure view and single mutant data analysis

Study data

No weblogo for data of varying length.
Colors: D E R H K S T N Q A V I L M F Y W C G P

Data Distribution

Studies with similar sequences (approximate matches)

Correlation with other assays (exact sequence matches)

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 Myoglobin P02185 MYG_PHYMC
96.8 Myoglobin Q0KIY5 MYG_KOGBR
96.8 Myoglobin P02184 MYG_KOGSI
92.9 Myoglobin Q0KIY1 MYG_BALBO
92.9 Myoglobin Q0KIY2 MYG_BALED
92.9 Myoglobin P02177 MYG_ESCRO
92.2 Myoglobin P02178 MYG_MEGNO
91.4 Myoglobin Q0KIY3 MYG_PENEL
91.4 Myoglobin P02181 MYG_INIGE
92.1 Myoglobin P02174 MYG_GLOME
90.9 Myoglobin P02179 MYG_BALAC
91.4 Myoglobin P02173 MYG_ORCOR
90.8 Myoglobin Q0KIY7 MYG1_STEAT
90.8 Myoglobin P68276 MYG_DELDE
90.8 Myoglobin P68279 MYG_TURTR
90.8 Myoglobin P68277 MYG_PHODA
90.8 Myoglobin P68278 MYG_PHOPH
90.3 Myoglobin P02180 MYG_BALPH
90.1 Myoglobin P02183 MYG_MESCA
90.1 Myoglobin Q0KIY0 MYG_MESST
90.1 Myoglobin P02182 MYG_ZIPCA