a b s t r a c tThe bacterial translational GTPases release factor RF3 promotes translation termination by recycling RF1 or RF2. Here, we present the crystal structures of RF3 complexed with GDP and guanosine 3 0 ,5 0 -(bis)diphosphate (ppGpp) at resolutions of 1.8 and 3.0 Å, respectively. ppGpp is involved in the socalled ''stringent response'' of bacteria. ppGpp binds at the same site as GDP, suggesting that GDP and ppGpp are two alternative physiologically relevant ligands of RF3. We also found that ppGpp decelerates the recycling of RF1 by RF3. These lines of evidence suggest that RF3 functions both as a cellular metabolic sensor and as a regulator.
A core–shell
ensemble of bovine hemoglobin (Hb) and human serum albumin (HSA) is
an artificial O2 carrier as a red blood cell substitute.
This protein particle is created by covalent wrapping of a carbonyl
Hb with HSAs: HbR–HSA
3
cluster, where HbR signifies the use of carbonyl Hb (relaxed
(R) state conformation) as a starting material. The HbR–HSA
3
cluster exhibits high O2 affinity and low cooperativity. Analysis of the quaternary
structure of the central HbR in the cluster revealed that
its high O2 affinity is attributed to the physically immobile
HbR nucleus. Circular dichroism and UV–vis absorption
spectroscopy showed that the structure of deoxy HbR core
closely resembles the R-state. The crystal structure of Lys-modified
carbonyl HbR was superimposed on that of carbonyl Hb. These
results imply that chemical modifications of the surface Lys groups
and Cys-93(β) of the carbonyl Hb with cross-linking agent interfered
in the quaternary structure movement from the R-state to tense (T)
state. As expected, coupling of deoxy Hb (T-state) with HSAs yielded
HbT–HSA
3
cluster having
low O2 affinity. The mixing of HbR–HSA
3
and HbT–HSA
3
clusters conferred a tailor-made formulation of
artificial O2 carrier with a desired O2 affinity
(P
50).
There is no blood bank for pet animals. Consequently, veterinarians themselves must obtain “blood” for transfusion therapy. Among the blood components, serum albumin and red blood cells (RBCs) are particularly important to save lives. This paper reports the synthesis, structure, and properties of artificial blood for the exclusive use of dogs. First, recombinant canine serum albumin (rCSA) was produced using genetic engineering with Pichia yeast. The proteins showed identical features to those of the native CSA derived from canine plasma. Furthermore, we ascertained the crystal structure of rCSA at 3.2 Å resolution. Pure rCSA can be used widely for numerous clinical and pharmaceutical applications. Second, hemoglobin wrapped covalently with rCSA, hemoglobin–albumin cluster (Hb-rCSA3), was synthesized as an artificial O2-carrier for the RBC substitute. This cluster possesses satisfactorily negative surface net charge (pI = 4.7), which supports enfolding of the Hb core by rCSA shells. The anti-CSA antibody recognized the rCSA exterior quantitatively. The O2-binding affinity was high (P50 = 9 Torr) compared to that of the native Hb. The Hb-rCSA3 cluster is anticipated for use as an alternative material for RBC transfusion, and as an O2 therapeutic reagent that can be exploited in various veterinary medicine situations.
Recombinant human haemoglobin expressed in Pichia yeast was wrapped covalently with recombinant human serum albumins, yielding a core–shell structured rHbA(X)–rHSA3 cluster as an entirely synthetic O2 carrier used for a red blood cell substitute.
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