PubMed · 9379924
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
D E Tronrud. 1997. TNT refinement package.. https://doi.org/10.1016/s0076-6879(97)77017-4
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
A series of reaction centres bearing mutations at the (Phe) M197 position were constructed in the photosynthetic bacterium Rhodobacter sphaeroides. This residue is adjacent to the pair of bacteriochlorophyll molecules (P(L) and P(M)) that is the primary donor of electrons (P) in photosynthetic light-energy transduction. All of the mutations affected the optical and electrochemical properties of the P bacteriochlorophylls. A mutant reaction centre with the change Phe M197 to Arg (FM197R) was crystallized, and a structural model constructed at 2.3 A (1 A=0.1 nm) resolution. The mutation resulted in a change in the structure of the protein at the interface region between the P bacteriochlorophylls and the monomeric bacteriochlorophyll that is the first electron acceptor (B(L)). The new Arg residue at the M197 position undergoes a significant reorientation, creating a cavity at the interface region between P and B(L). The acetyl carbonyl substituent group of the P(M) bacteriochlorophyll undergoes an out-of-plane rotation, which decreases the edge-to-edge distance between the macrocycles of P(M) and B(L). In addition, two new buried water molecules partially filled the cavity that is created by the reorientation of the Arg residue. These waters are in a suitable position to connect the macrocycles of P and B(L) via three hydrogen bonds. Transient absorption measurements show that, despite an inferred decrease in the driving force for primary electron transfer in the FM197R reaction centre, there is little effect on the overall rate of the primary reaction in the bulk of the reaction-centre population. Examination of the X-ray crystal structure reveals a number of small changes in the structure of the reaction centre in the interface region between the P and B(L) bacteriochlorophylls that could account for this faster-than-predicted rate of primary electron transfer.
Seven hyper-stable multiple mutants have been constructed in staphylococcal nuclease by various combinations of eight different stabilizing single mutants. The stabilities of these multiple mutants determined by guanidine hydrochloride denaturation were 3.4 to 5.6 kcal/mol higher than that of the wild-type. Their thermal denaturation midpoint temperatures were 12.6 to 22.9 deg. C higher than that of the wild-type. These are among the greatest increases in protein stability and thermal denaturation midpoint temperature relative to the wild-type yet attained. There has been great interest in understanding how proteins found in thermophilic organisms are stabilized. One frequently cited theory is that the packing of hydrophobic side-chains is improved in the cores of proteins isolated from thermophiles when compared to proteins from mesophiles. The crystal structures of four single and five multiple stabilizing mutants of staphylococcal nuclease were solved to high resolution. No large overall structural change was found, with most changes localized around the sites of mutation. Rearrangements were observed in the packing of side-chains in the major hydrophobic core, although none of the mutations was in the core. It is surprising that detailed structural analysis showed that packing had improved, with the volume of the mutant protein's hydrophobic cores decreasing as protein stability increased. Further, the number of van der Waals interactions in the entire protein showed an experimentally significant increase correlated with increasing stability. These results indicate that optimization of packing follows as a natural consequence of increased protein thermostability and that good packing is not necessarily the proximate cause of high stability. Another popular theory is that thermostable proteins have more electrostatic and hydrogen bonding interactions and these are responsible for the high stabilities. The mutants here show that increased numbers of electrostatic and hydrogen bonding interactions are not obligatory for large increases in protein stability.
Norbornene-supported bis-helical peptides with the general structure NBE(Aib(n) )(2) (NBE: 2,3-trans-norbornene dicarbonyl unit; Aib: alpha,alpha'-dimethyl glycine unit; n = 4,5) have been synthesized and examined for self-assembly preferences in the solid state. An x-ray study has revealed a phenomenon of Janus helicity in the solid state structure of NBE(Aib(5))(2). The lower homologue NBE(Aib(4))(2), however, shows an identical screw sense for both the helical arms. The difference in the handedness of left and right arms is reflected in the self-assembly patterns. Thus, while the NBE(Aib(4))(2) molecule self-assembles to form an infinite hydrogen-bonded superhelical ladder, the Janus molecule NBE(Aib(5))(2) crystallizes as individual units surrounded by water molecules. The structures of Z-Aib(4)-OMe and Z-Aib(5)-OMe are also presented to compare their conformations with the helical arms of the title compound and also to the already known structures of other X-Aib(n) -Y compounds. The helices in all the molecules are the 3(10)-type.