title: Importance of the C-terminal loop L137-S141 for the folding and folding stability of staphylococcal nuclease.
abstract: The role of the C-terminal loop L137-S141 in the folding and folding stability of staphylococcal nuclease (SNase) was investigated by deletion mutation. The C-terminal truncated SNase fragments, SNase137, SNase139, SNase140, and SNase141 containing residues 1-137, 1-139, 1-140, and 1-141, respectively, were adopted in this study. Folding states of these four SNase fragments were analyzed by circular dichroism and fluorescence measurements. The solution structure of SNase140 was determined and compared to those of SNase141 and native SNase using the heteronuclear NMR method. The results showed that folding of the four SNase fragments is correlated with the folding of helix alpha3. With the chain length extending from L137 and I139 to S141, folding of the fragments progressively approached to the tertiary folding of native SNase, and the folding stability was enhanced. These observations revealed that the C-terminal loop L137-S141 has profound effect not only on the folding of helix alpha3 but also on the stabilizing folding of both the alpha- and beta-subdomains of SNase. Analysis indicates that stabilizing folding of the SNase and SNase fragments depends to a large extent on the hydrophobic packing interactions in both the C-terminal local structural region surrounding W140 including the loop L137-S141 and the N-terminal local structural region of the "beta-barrel" hydrophobic core.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
authors.forename: Min
authors.initials: M
authors.lastname: Wang
authors.forename: Yingang
authors.initials: Y
authors.lastname: Feng
authors.forename: Hongwei
authors.initials: H
authors.lastname: Yao
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Wang
mesh_terms: D004789:Enzyme Activation; D057927:Hydrophobic and Hydrophilic Interactions; D008836:Micrococcal Nuclease / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000502:physiology; D014508:Urea / Q000494:pharmacology
chemical_list: D010446:Peptide Fragments; D014508:Urea; D008836:Micrococcal Nuclease