کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
5371408 1388818 2011 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
The soluble, periplasmic domain of OmpA folds as an independent unit and displays chaperone activity by reducing the self-association propensity of the unfolded OmpA transmembrane β-barrel
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی تئوریک و عملی
پیش نمایش صفحه اول مقاله
The soluble, periplasmic domain of OmpA folds as an independent unit and displays chaperone activity by reducing the self-association propensity of the unfolded OmpA transmembrane β-barrel
چکیده انگلیسی

OmpA is one of only a few transmembrane proteins whose folding and stability have been investigated in detail. However, only half of the OmpA mass encodes its transmembrane β-barrel; the remaining sequence is a soluble domain that is localized to the periplasmic side of the outer membrane. To understand how the OmpA periplasmic domain contributes to the stability and folding of the full-length OmpA protein, we cloned, expressed, purified and studied the OmpA periplasmic domain independently of the OmpA transmembrane β-barrel region. Our experiments showed that the OmpA periplasmic domain exists as an independent folding unit with a free energy of folding equal to − 6.2 (± 0.1) kcal mol-1 at 25 °C. Using circular dichroism, we determined that the OmpA periplasmic domain adopts a mixed alpha/beta secondary structure, a conformation that has previously been used to describe the partially folded non-native state of the full-length OmpA. We further discovered that the OmpA periplasmic domain reduces the self-association propensity of the unfolded barrel domain, but only when covalently attached (in cis). In vitro folding experiments showed that self-association competes with β-barrel folding when allowed to occur before the addition of membranes, and the periplasmic domain enhances the folding efficiency of the full-length protein by reducing its self-association. These results identify a novel chaperone function for the periplasmic domain of OmpA that may be relevant for folding in vivo. We have also extensively investigated the properties of the self-association reaction of unfolded OmpA and found that the transmembrane region must form a critical nucleus comprised of three molecules before undergoing further oligomerization to form large molecular weight species. Finally, we studied the conformation of the unfolded OmpA monomer and found that the folding-competent form of the transmembrane region adopts an expanded conformation, which is in contrast to previous studies that have suggested a collapsed unfolded state.

Highlights► The OmpA periplasmic domain folds as an independent domain. ► The OmpA periplasmic domain displays chaperone activity by increasing folding efficiency. ► The unfolded OmpA beta-barrel contains no regular secondary structure and is expanded.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Biophysical Chemistry - Volume 159, Issue 1, November 2011, Pages 194-204
نویسندگان
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