Thermodynamics of hCG--monoclonal antibody interaction: an analysis of real time kinetics data obtained using radiolabeled hCG probe

Development of a radiolabeled beta-human chorionic gonadotropin

beta-Human chorionic gonadotropin (beta-hCG) was successively labeled with [(67)Ga]-gallium chloride after conjugation with freshly prepared diethylenetriaminepentaacetic acid dianhydride (ccDTPA). After solid phase purification of the radiolabeled hormone, high performance liquid chromatography showed radiochemical purity higher than 95 % under optimized conditions (specific activity = 22-23 TBq mM(-1), labeling efficiency 80 %). Preliminary in vivo studies (ID g(-1), %) in male wild-type rats showed marked gonadal uptake of the tracer after 240 minutes in agreement with the biodistribution studies and reported beta-hCG receptors. Target to blood ratios were 5.1 and 15.2 after 3 and 24 hours, respectively, while target to muscle ratios were 35 and 40 after 3 and 24 hours, respectively.

Epitope mapping from real time kinetic studies - role of crosslinked disulphides and incidental interacting regions in affinity measurements: study with human chorionic gonadotropin and monoclonal antibodies

Real time kinetic studies were used to map conformational epitopes in human chorionic gonadotropin (hCG) for two monoclonal antibodies (MAbs). The epitopes were identified in the regions (alpha 5--14 and alpha 55--62). The association rate constant (k+1) was found to be altered by chemical modification of hCG, and the ionic strength of the reaction medium. Based on these changes, we propose the presence of additional interactions away from the epitope- paratope region in the hCG-MAb reaction. We have identified such incidental interacting regions (IIRs) in hCG to be the loop region alpha 35--47 and alpha 60--84. The IIRs contribute significantly towards the KA of the interaction. Therefore, in a macromolecular interaction of hCG and its MAb, KA is determined not only by epitopeparatope interaction but also by the interaction of the nonepitopic-nonparatopic IIRs. However, the specificity of the interaction resides exclusively with the epitope-paratope pair.

The Novel Drosophila Lysosomal Enzyme Receptor Protein Mediates Lysosomal Sorting in Mammalian Cells and Binds Mammalian and Drosophila GGA Adaptors

Biogenesis of lysosomes depends in mammalian cells on the specific recognition and targeting of mannose 6-phosphate-containing lysosomal enzymes by two mannose 6-phosphate receptors (MPR46, MPR300), key components of the extensively studied receptor-mediated lysosomal sorting system in complex metazoans. In contrast, the biogenesis of lysosomes is poorly investigated in the less complex metazoan Drosophila melanogaster. We identified the novel type I transmembrane protein lysosomal enzyme receptor protein (LERP) with partial homology to the mammalian MPR300 encoded by Drosophila gene CG31072. LERP contains 5 lumenal repeats that share homology to the 15 lumenal repeats found in all identified MPR300. Four of the repeats display the P-lectin type pattern of conserved cysteine residues. However, the arginine residues identified to be essential for mannose 6-phosphate binding are not conserved. The recombinant LERP protein was expressed in mammalian cells and displayed an intracellular localization pattern similar to the mammalian MPR300. The LERP cytoplasmic domain shows highly conserved interactions with Drosophila and mammalian GGA adaptors known to mediate Golgi-endosome traffic of MPRs and other transmembrane cargo. Moreover, LERP rescues missorting of soluble lysosomal enzymes in MPR-deficient cells, giving strong evidence for a function that is equivalent to the mammalian counterpart. However, unlike the mammalian MPRs, LERP did not bind to the multimeric mannose 6-phosphate ligand phosphomannan. Thus ligand recognition by LERP does not depend on mannose 6-phosphate but may depend on a common feature present in mammalian lysosomal enzymes. Our data establish a potential important role for LERP in biogenesis of Drosophila lysosomes and suggest a GGA function also in the receptor-mediated lysosomal transport system in the fruit fly.

Vibration enhancement of slide-mounted immunofluorescence staining

Immunofluorescence techniques allow the determination of protein and small molecule distribution within tissues and individual cells. There have been important, innovative modifications of these techniques since their introduction to the biosciences including the use of a mounting medium that prevents photo-bleaching, non-ionic detergents to permeabilize membranes, multiple immunofluorescence labeling and antigen recovery techniques for optimizing ligand-target interactions. While methods have been optimized for ligand-target accessibility in free-floating sections, little innovation has occurred to improve antibody access and epitope recognition in immunohistochemistry on slide-mounted sections or cell culture. During our studies of brain signaling pathways, we sought to improve the immunofluorescence signal to noise ratio in these specimens. We present here a minor modification of immunofluorescence procedures that significantly increases antibody access to epitopes within tissue and improves staining quality while significantly shortening incubation time. Antibody-epitope interactions are dependent on access and affinity. Our technique is based upon application of a vibration source during antibody incubation which increases epitope access, shortens incubation time and thereby minimizes background immunofluorescence. Data are presented on benefits evident with several antibodies raised against proteins and peptides localized in various subcellular compartments. Analysis of the quality of labeling was performed to show that signal intensity is enhanced and background intensity is often diminished when incubations are performed under gentle vibration. This, together with the significant saving of time, should make this procedure applicable to a wide range of neurobiological questions.