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Biomedical subjects

Z C Fan

Publications and source records attributed to Z C Fan.

7 recordsLinked to original sources
PubMed1996

[Study on drawing aseptic gas in diluting drugs].

In this study, the gas was drawn from sealed aseptic bottles, the blue flame of an alcohol lamp, and the air of the same treatment room. And the gas was put into aseptic solutions of 10% glucose separately and dripped. Then the samples were taken for bacteriaculture at appointed time-points. Meanwhile, the gases were drawn and put into aseptic solutions of 10% glucose separately. Then deactived penicillines were diluted with the solutions separately. Finally, the penicillines were mixed with 10% glucose and dripped. The samples were taken for bacteria-culture in the same way. The results showed that there was no colony existed in the gas from the sealed aseptic bottles and the flame of the alcohol lamp. However, colonies existed in the samples from the air of the treatment room. It is suggested that sealed aseptic gas should be drawn and kept for use in diluting drugs.

Asepsis↗
PubMed1995

Intramolecular signaling upon complexation.

Crystal habits can be used as indicators of conformational changes in their constituent proteins. As in the conversion of unliganded hemoglobin to the oxygenated form, the addition of a small hapten to a suspension of platy crystals of an unliganded Fab (NC6.8) results in the immediate disintegration of the plates and their replacement with prisms of the ligand-protein complex. Examination of the native and liganded forms by X-ray crystallography reveals that the space groups and protein structures are different. During complexation there are ligand-induced conformational changes both in the antigen combining site (local alterations) and in more distal portions of the molecule (allosteric changes). There is an extension of the light chain (10 A increase in length), a commensurate shortening of the heavy chain (by flexing), and a decrease in the "elbow bend" angle of 31 degrees (184 degrees to 153 degrees). Relative to the variable domains, the constant domain pair moves mainly as a unit in such a way that the carboxyl end of the heavy chain is displaced by 19 A. In an intact antibody this displacement may be relayed as a tug (by tensile forces) on the segment connecting the Fab to the Fc region, perhaps altering the orientations of the constituents responsible for such effector functions as complement activation.

Animals↗
PubMed1993

Principles and pitfalls in designing site-directed peptide ligands.

An immunoglobulin light chain dimer with a large generic binding cavity was used as a host molecule for designing a series of peptide guest ligands. In a screening procedure peptides coupled to solid supports were systematically tested for binding activity by enzyme linked immunosorbent assays (ELISA). Key members of the binding series were synthesized in milligram quantities and diffused into crystals of the host molecule for X-ray analyses. These peptides were incrementally increased in size and affinity until they nearly filled the cavity. Progressive changes in binding patterns were mapped by comparisons of crystallographically refined structures of 14 peptide-protein complexes at 2.7 A resolution. These comparisons led to guidelines for ligand design and also suggested ways to modify previously established binding patterns. By manipulating equilibria involving histidine, for example, it was possible to abolish one important intramolecular interaction of the bound ligand and substitute another. These events triggered a change in conformation of the ligand from a compact to an extended form and a comprehensive change in the mode of binding to the protein. In dipeptides of histidine and proline, protonation of both imidazolium nitrogen atoms was used to program an end-to-end reversal of the direction in which the ligand was inserted into the binding cavity. Peptides cocrystallized with proteins produced complexes somewhat different in structure from those in which ligands were diffused into preexisting crystals. In such a large and malleable cavity, space utilization was thus different when a ligand was introduced before the imposition of crystal packing restraints.

Bence Jones Protein↗
PubMed1992

Three-dimensional structure of an Fv from a human IgM immunoglobulin.

An IgM(kappa) immunoglobulin from a patient (Pot) with Waldenstrom's macroglobulinemia was hydrolyzed with pepsin to release a fragment consisting of the 'variable' (V) domains of the light and heavy chains plus eight residue 'tails' from the 'constant' (C) domains. The crystal structure of this fragment was determined at 2.3 A resolution by molecular replacement and crystallographic refinement methods. When examined separately, the light chain component closely resembles another human kappa chain (Rei) in both the beta-pleated sheet regions and the 'hypervariable' loops. The conserved pleated sheets in the heavy chain are similar to those in the human Kol IgG1 protein, but the third hypervariable loop in particular is different from that in any immunoglobulin structure described to date. As in the Kol protein, this loop blocks the access to any internal active site along the light-heavy chain interface. Unlike the Kol protein, however, the loop does not protrude beyond the boundaries of a conventional antigen combining site. Instead, it forms a very compact structure, which fills almost all residual space between the domains. This is an example of one dominant complementarity-determining region (CDR) essentially negating the diversity possible with five other CDRs in the two chains. Ordered water molecules are associated with light chain constituents along the interface, but not with CDR3 of the heavy chain. In screening exercises the Pot IgM failed to bind a wide variety of peptides. Together, the results suggest that ligand binding can only occur on external surfaces of the protein. These surfaces carry a limited number of side chains usually assigned to CDRs in more typical antibodies.

Amino Acid Sequence↗
PubMed1991

[Clinical and experimental research on prevention and treatment of child reversal respiratory tract infection by feibao].

This article reports the child reversal respiratory tract infection treated with Feibao syrup which produced in accordance with the TCM theory of "the evil factor can't attack the body with vital-Qi" and "the evil factor will attack the body which vital-Qi is weak". Feibao syrup consisted of Radix Astragali, Herba Hedyotis diffusae, etc. The clinical research proved that after taking the medicine, the general condition, appetite and anemia were improved, the profuse sweating disappeared, the tolerance against cold was improved, the frequency of occurrence of the disease was decreased or ceased. Even if the disease occurred, the symptoms were mild, the disease course was short. The efficacy of the medicine was 95.2%. It was better than that of levamisole (78.6%), P less than 0.05. This medicine can obviously improve the level of serum IgA and the cellular immunity (P less than 0.01). The experiment on mice manifested that it could obviously enhance the macrophage phagocytic rate, lymphocyte transformation rate, EAC rosette forming rate, and hemolysin generating rate.

Animals↗
PubMedDate not supplied

Comparison of the three-dimensional structures of a humanized and a chimeric Fab of an anti-gamma-interferon antibody.

The objective of this work is to compare the three-dimensional structures of "humanized" and mouse-human chimeric forms of a murine monoclonal antibody elicited against human gamma-interferon. It is also to provide structural explanations for the small differences in the affinities and biological interactions of the two molecules for this antigen. Antigen-binding fragments (Fabs) were produced by papain hydrolysis of the antibodies and crystallized with polyethylene glycol (PEG) 8,000 by nearly identical microseeding procedures. Their structures were solved by X-ray analyses at 2.9 A resolution, using molecular replacement methods and crystallographic refinement. Comparison of these structures revealed marked similarities in the light (L) chains and near identities of the constant (C) domains of the heavy (H) chains. However, the variable (V) domains of the heavy chains exhibited substantial differences in the conformations of all three complementarity-determining regions (CDRs), and in their first framework segments (FR1). In FR1 of the humanized VH, the substitution of serine for proline in position 7 allowed the N-terminal segment (designated strand 4-1) to be closely juxtaposed to an adjacent strand (4-2) and form hydrogen bonds typical of an antiparallel beta-pleated sheet. The tightening of the humanized structure was relayed in such a way as to decrease the space available for the last portion of HFR1 and the first part of HCDR1. This compression led to the formation of an alpha-helix involving residues 25-32. With fewer steric constraints, the corresponding segment in the chimeric Fab lengthened by at least 1 A to a random coil which terminated in a single turn of 310 helix. In the humanized Fab, HCDR1, which is sandwiched between HCDR2 and HCDR3, significantly influenced the structures of both regions. HCDR2 was forced into a bent and twisted orientation different from that in the chimeric Fab, both at the crown of the loop (around proline H52a) and at its base. As in HCDR1, the last few residues of HCDR2 in the humanized Fab were compressed into a space-saving alpha-helix, contrasting with a more extended 310 helix in the chimeric form. HCDR3 in the humanized Fab was also adjusted in shape and topography. The observed similarities in the functional binding activities of the two molecules can be rationalized by limited induced fit adjustments in their structures on antigen binding. While not perfect replicas, the two structures are testimonials to the progress in making high affinity monoclonal antibodies safe for human use.

Amino Acid Sequence↗