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ANALYTICAL CURRENTS ECD-MS details protein folding
Delay/s
the weaker noncovalent bonds. Statistical vation and are inhibited by tertiary nonProbably the most unlikely method for covalent bonding across a cleavage site. analysis finds that ECD cleavages are studying noncovalent bonding in gasThe cleavage reaction produces priphase biomolecules is electron-capture dis- largely indifferent to the identity of the marily one type of product ion (~90% adjacent amino acids, but they favor prosociation (ECD) MS. Yet, Fred McLafferc,z*). If two fragments from a (M + tonation sites with secondary-charge solty and his colleagues at Cornell University nH)n+ ion are still joined by show that ECD-MS yields noncovalent bonding data for noncovalent bonds, they ap30.0 69 of 75 interresidue locations pear in the spectrum as the in gaseous bovine ubiquitin reduced molecular ion (M + 5.0 protein ions, which are then nH)(n–1)+•. These data are used to determine thermal unthen used to determine 1.0 folding enthalpies, conformaabundances of folded and tional melting temperatures, unfolded ions and equilibria; 0.17 and kinetics of pulsed laser uncollecting these data at varifolding and refolding. Their ous temperatures provides 0.07 results support a “folding fununfolding enthalpies. nel” mechanism, in which Despite their success, the no laser conformational changes inauthors warn that it is unreavolve numerous intermediates sonable to expect a close struc0 10 20 30 40 50 60 70 and parallel reaction pathways. tural relationship between the Cleavage site The surprise in the method native conformer of any prois that ECD dissociates covaUnfolding and refolding kinetics of ubiquitin 7+ ions at 25 ºC from elec- tein and its gaseous counterlent protein backbone bonds tron-capture dissociation spectra. The left column shows the intervals parts. (J. Am. Chem. Soc. 2002, without appreciably affecting 124, 6407–6420) after pulsed IR-laser excitation.
Multitalented nanogels People say you can’t teach an old dog new
nanogel is more stable at a high tempera-
ly, the nanogels were smallest when tem-
tricks, but Dirk Kuckling and colleagues at
ture or low pH than the core nanogel
perature and pH were high because both
Technische Universität Dresden (Germany)
alone.
regions collapsed. Nanogels with a col-
have endowed a temperature-sensitive
The nanogels had the largest diameters
lapsed core and swollen shell generally
nanogel with pH sensitivity, too. This dual-
when both temperature and pH were low
had smaller average hydrodynamic diame-
purpose nanogel responds to the two stim-
because the core and pH-sensitive shell
ters than nanogels with a swollen core and
uli independently.
swelled under those conditions. Converse-
collapsed shell. The researchers say that
The researchers synthe-
this happens because the
size the new nanogels by
gels contained more core-
adding pH-sensitive poly(2-
UV light
forming polymer than shell-
vinylpryidine) arms to temper-
forming polymer and because
ature-sensitive poly(N-iso-
the volume effect influences
propylacrylamide)-based nanogel cores and irradiating them with UV light. The hybrid 406 A
The stages of preparation of nanogels with temperature-sensitive cores and pH-sensitive shells. In both steps, the temperature is greater than the lower critical solution temperature, which is the minimum temperature needed for phase separation.
A N A LY T I C A L C H E M I S T R Y / A U G U S T 1 , 2 0 0 2
the core diameter more strongly. (Langmuir 2002, 18, 4263–4269)
