Human prostatic acid phosphatase: purification, characterization, and optimization of conditions for radioimmunoassay

Purification, identification and Cryo-EM structure of prostatic acid phosphatase in human semen

Prostatic acid phosphatase (PAP) is a glycoprotein that plays a crucial role in the hydrolysis of phosphate ester present in prostatic exudates. It is a well-established indicator for prostate cancer due to its elevated serum levels in disease progression. Despite its abundance in semen, PAP's influence on male fertility has not been extensively studied. In our study, we report a significantly optimized method for purifying human endogenous PAP, achieving remarkably high efficiency and active protein recovery rate. This achievement allowed us to better analyze and understand the PAP protein. We determined the cryo-electron microscopic (Cryo-EM) structure of prostatic acid phosphatase in its physiological state for the first time. Our structural and gel filtration analysis confirmed the formation of a tight homodimer structure of human PAP. This functional homodimer displayed an elongated conformation in the cryo-EM structure compared to the previously reported crystal structure. Additionally, there was a notable 5-degree rotation in the angle between the α domain and α/β domain of each monomer. Through structural analysis, we revealed three potential glycosylation sites: Asn94, Asn220, and Asn333. These sites contained varying numbers and forms of glycosyl units, suggesting sugar moieties influence PAP function. Furthermore, we found that the active sites of PAP, His44 and Asp290, are located between the two protein domains. Overall, our study not only provide an optimized approach for PAP purification, but also offer crucial insights into its structural characteristics. These findings lay the groundwork for further investigations into the physiological function and potential therapeutic applications of this important protein.

Clinical and biological aspects of acid phosphatase

The identity and genetic origins of the nonspecific orthophosphate monoesterases with an acid pH optimum--the acid phosphatases--are now becoming clear. They form a family of genetically distinct isoenzymes, many of which show significant posttranslational modification. Four true isoenzymes exist. The erythrocytic and lysosomal forms show widespread distribution and are expressed in most cells; in contrast, the prostatic and macrophagic forms have a more limited expression. The erythrocytic and macrophagic forms are distinguished from the others in resisting inhibition by dextrorotatory tartrate. The prostatic form has long been used as a marker for prostatic cancer and the macrophagic forms have been linked with miscellaneous disorders, notably increased osteolysis, Gaucher's disease of spleen, and hairy cell leukemia, whereas the normal levels of intravesical lysosomal acid phosphatase in I cell disease pointed the way toward the mechanisms underlying its intracellular processing.

A reference preparation of human prostatic acid phosphatase: purification, characterization and field trials

Acid phosphatase has been prepared in an apparently pure state by affinity chromatography from human prostatic tissue. When dissolved in an acidic albumin solution, lyophilized and stored at -20 degrees C for up to 2 years, no time-dependent loss of catalytic activity was detectable in the reconstituted material. Accelerated degradation tests also predicted complete stability. A preliminary distribution of the lyophilized preparation to 143 laboratories confirmed its robustness and demonstrated its potential usefulness as a calibrant to unify the results of different methods of measuring acid phosphatase activity.

The evaluation of markers of prostatic function

The concentrations of three secretory proteins of the human prostate, including prostatic secretory protein of 94 amino acid residues (PSP94), prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP), were measured by enzyme-linked immunosorbent assay (ELISA) in semen from a collective of patients suffering from various inflammatory diseases of the genital tract. In addition, levels of the conventional markers citrate, glucosidase and fructose were determined. As compared with semen from men exhibiting no inflammatory condition, only levels of glucosidase in cases of epididymitis and concentrations of PSP94 in the collective suffering from prostatitis showed significant reductions. The changes in the secretion of PSA, PAP, fructose and citrate in the semen of patients with inflammation of genital tract tissue were not significant at the 95% range of confidence.

Characterization of a monoclonal antibody specific for prostatic secretory protein of 94 amino acids (PSP94) and development of a two-site binding enzyme immunoassay for PSP94

Purified prostatic secretory protein of 94 amino acids (PSP94) was used to generate polyclonal rabbit anti-PSP94 IgG and a murine monoclonal antibody 6B6 (mAB6B6). Both antibodies were highly specific for PSP94 by immunoblotting. Immunohistochemical studies demonstrated the specificity of mAB6B6 for human prostatic epithelial tissue. A two-site binding enzyme immunoassay for the detection of PSP94 was developed using a combination of the antibodies. The sandwich-ELISA yielded satisfactory results when mAB6B6 complexed to peroxidase conjugated goat anti-mouse-IgG (Fc) was incubated simultaneously with the sample. The assay has a dynamic range of 2-30 micrograms/l. This immunoassay was employed to measure PSP94 in male human sera (8 +/- 4 micrograms/l), female human sera (5.7 +/- 3.4 micrograms/l), follicular fluid (3.9 +/- 2.9 micrograms/l) and human seminal plasma (1.02 +/- 0.8 g/l).

Three predominant proteins secreted by the human prostate gland

Analyses of the proteins of azoospermic ejaculates from subjects with defective seminal vesicles demonstrated that three prostatic-secreted proteins were predominant. Prostatic acid phosphatase (PAP), prostate-specific antigen (PSA; or gamma-seminoprotein), and beta-microseminoprotein (beta-MSP; or beta-inhibin), were identified as the three predominant proteins secreted by the normal human prostate gland. Immunohistochemical localization of these proteins, in the epithelium of normal prostatic acini and ducts, with the avidin-biotin complex procedure demonstrated that each PAP-immunoreactive cell was invariably immunoreactive both with PSA-and beta-MSP-monospecific antisera as well.

Significance of serum protein and lipid-bound sialic acid as a marker for genitourinary malignancies

A prospective study was done to evaluate the roles of serum N-acetylneuraminic acid (NANA) and the lipid-bound subfraction of sialic acid (LSA) concentrations in the detection and staging of cancer, and the follow-up of treatment in patients with genitourinary malignancies. Multiple determinations were obtained in 177 subjects: 90 normal volunteers, 38 patients with prostate cancer, 20 patients with bladder cancer, 15 patients with renal cell cancer, and 14 patients with benign urologic diseases. The results showed a low incidence of elevated values in patients with early stages of cancer and a high incidence of false-positive values with serum NANA concentrations in patients with benign urologic diseases, especially prostatitis. Serum NANA and LSA concentrations were highly correlated with the stage and grade in patients with advanced urologic cancer, and may be used as markers of tumor activity during follow-up under treatment; currently, however, they are not useful in the screening of patients for urologic cancer. Their usefulness in prostatic cancer is at least comparable to that of acid phosphatase determinations by the enzymatic and radioimmunoassay methods, which were elevated in a smaller percentage of patients with prostate cancer than were the NANA or LSA concentrations.

Biochemical nature of the prostate-associated antigen identified by the monoclonal antibody, KR-P8

The KR-P8 monoclonal antibody identifies an organ-specific antigen that is associated with normal as well as malignant specimens of human prostate tissue. The antigen is secreted by cells of the prostate and is present in samples of seminal plasma. Data presented here describe the biochemical nature of the antigen that is recognized by KR-P8 as it occurs in seminal plasma and in extracts prepared from cells of the prostate tumor line, PC3. Antigen contained in seminal plasma migrated as a broad band on SDS-polyacrylamide gels in the molecular weight range of 48,000-75,000 d. A similar pattern was observed for antigen prepared from detergent extracts of PC3 cells. The antigen was found to be sensitive to treatment with trypsin and chymotrypsin and the contribution of carbohydrate residues to the structure of the molecule was shown by studies that demonstrated binding of the antigen to Concanavalin A and Soybean Agglutinin lectins. Loss of antigenicity subsequent to periodate oxidation suggested that carbohydrate units are involved in the recognition site for KR-P8 on the antigen.

Characterization of human prostatic acid phosphatase radioiodinated by four different procedures

Prostatic acid phosphatase was labeled by four different iodination procedures: chloramine-T, insoluble or soluble lactoperoxidase, and Bolton-Hunter. Enzyme labeled by the chloramine-T procedure had suboptimal precipitation characteristics in immunoassays, with 36 to 67% of the tracer precipitated in antibody excess. Analysis of the tracer on 7.5% sodium dodecyl sulfate polyacrylamide gel showed that as much as 30% of the radioactivity migrated away from the protein within 6 minutes after the electrophoretic run was begun. The nature of this fast migrating radioiodinated component was not determined. The failure to obtain a tracer labeled by the chloramine-T procedure with optimal immunoprecipitation characteristics led to investigation of alternate radioiodination procedures. Insoluble or soluble lactoperoxidase was less effective than chloramine-T in producing a tracer suitable for radioimmunoassay. In contrast, the Bolton-Hunter procedure produced a tracer that had optimal precipitation characteristics; 88 to 91% of the tracer was precipitated in antibody excess. The tracer was further purified by affinity chromatography to minimize the possibility of other protein contaminants compromising the specificity of a radioimmunoassay for the enzyme.