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N Zheng

Publications and source records attributed to N Zheng.

23 records · Page 2Linked to original sources
PubMed1997

Domain interactions in E. coli SRP: stabilization of M domain by RNA is required for effective signal sequence modulation of NG domain.

The E. coli protein, Fth, binds to 4.5S RNA through its M domain to form the signal recognition particle (SRP). The other domain of Fth (NG) is a GTPase, which binds and is coordinately regulated by its receptor, FtsY. We find that the helical M domain is inherently flexible. Binding of 4.5S RNA to Fth stabilizes the M domain yet has little apparent effect on the binding of signal peptides. However, in the absence of the RNA, signal peptide binding results in a global destabilization of Fth, which is prevented by binding of 4.5S RNA. Signal peptide binding to isolated NG domain also causes a pronounced destabilization, implicating the NG domain in direct recognition of signal peptide.

Amino Acid Sequence↗
PubMed1995

Scanning tunneling microscopy study of poly-L-proline.

Differences in its peptide bonds allow the imino acid poly-L-proline to exist in two significantly different geometric structures. Form I with cis peptide bonds is supposed to be a right-handed helix and form II with trans peptide bonds a left-handed helix. Cis/trans isomerization about the proline imide is believed to cause the denaturation of a number of proteins and may be a key step in protein folding. Using scanning tunneling microscopy (STM), we present high-resolution images of air-dried poly-L-proline. It is found that the electric conductivity of one monolayer of poly-L-proline is sufficient to allow for STM imaging without significant tip-sample interaction. Only at locations where stacking of poly-L-proline chains occurs, a direct contact of the probing tip to the molecules becomes apparent and prevents us, at present, from resolving the atomic structure of the topmost layer. Our STM images of poly-L-proline show that form II is relatively rigid and forms aggregates in most cases. Form I, which is occasionally observed, is very flexible and exhibits sharp bends as well as 180 degrees backfolding. These observations confirm theoretical predictions on the existence of two peptide bond conformations of poly-L-proline.

Isomerism↗
PubMedDate not supplied

Molecularly imprinted polymers from nicotinamide and its positional isomers.

Imprinted polymers were prepared for nicotinamide and its positional isomers. The influence of porogenic solvent and functional monomer on recognition properties of the polymer was compared. The results indicated that two functional groups, the heterocyclic nitrogen and the amide group, in the nicotinamide or isonicotinamide molecule have a synergistic effect in binding to the polymer. The polymers prepared with nicotinamide and isonicotinamide can be used as HPLC stationary phase for the separation of positional isomers of nicotinamide or isonicotinamide, while the polymer prepared with picolinamide showed no specificity toward the template. The mechanisms for the differences in recognition are discussed. In addition to the retention of polymers to their templates the polymers also displayed excellent retention to nicotinic acid and isonicotinic acid, compounds structurally similar to the template. This dual recognition property of the polymer may be useful in circumstances where the preparation of a polymer for a specific template may be problematic because of poor stability or solubility.

Amides↗
PubMedDate not supplied

Relationship of ulnar collateral ligament strain to amount of medial olecranon osteotomy.

Athletes at risk for valgus extension overload are also at risk for tears of the anterior bundle of the ulnar collateral ligament. Some athletes develop ligament tears after procedures for valgus extension overload such as posteromedial olecranon osteotomy. The amount of posteromedial olecranon that can be resected before ulnar collateral ligament strain, and risk of injury, increases is unknown. We dissected and mounted five fresh-frozen human cadaveric elbows to allow strain gauge monitoring of the ulnar collateral ligament with varying valgus stress, elbow flexion angle, and medial osteotomy. The average strain to failure was 11.96%+/-6.51%, corresponding to a load of 347.71+/-46.42 N. The maximum tensile force recorded at failure was 416.24 N. Three-way repeated-measures analysis of variance revealed no significant change in strain with change in the amount of osteotomy for a given applied load and angle of flexion. On the basis of these data, we conclude that the effect of medial olecranon osteotomy on ulnar collateral ligament strain may be small. Small sample size, elderly specimens, and the variables inherent in the experimental setup and mathematical modeling make it difficult to extrapolate these results to in vivo behavior of the anterior ulnar collateral ligament. Further work is needed before definitive guidelines for olecranon osteotomy can be formulated.

Collateral Ligaments↗