A pitfall in diagnosis of human prion diseases using detection of protease-resistant prion protein in urine: Contamination with bacterial outer membrane proteins

Hisako Furukawa, Katsumi Doh-Ura, Ryo Okuwaki, Susumu Shirabe, Kazuo Yamamoto, Heiichiro Udono, Takashi Ito, Shigeru Katamine, Masami Niwa

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

Because a definite diagnosis of prion diseases relies on the detection of the abnormal isoform of prion protein (PrPSc), it has been urgently necessary to establish a non-invasive diagnostic test to detect PrP Sc in human prion diseases. To evaluate diagnostic usefulness and reliability of the detection of protease-resistant prion protein in urine, we extensively analyzed proteinase K (PK)-resistant proteins in patients affected with prion diseases and control subjects by Western blot, a coupled liquid chromatography and mass spectrometry analysis, and N-terminal sequence analysis. The PK-resistant signal migrating around 32 kDa previously reported by Shaked et al. (Shaked, G. M., Shaked, Y., Kariv-Inbal, Z., Halimi, M., Avraham, I., and Gabizon, R. (2001) J. Biol. Chem. 276, 31479-31482) was not observed in this study. Instead, discrete protein bands with an apparent molecular mass of ∼37 kDa were detected in the urine of many patients affected with prion diseases and two diseased controls. Although these proteins also gave strong signals in the Western blot using a variety of anti-PrP antibodies as a primary antibody, we found that the signals were still detectable by incubation of secondary antibodies alone, i.e. in the absence of the primary anti-PrP antibodies. Mass spectrometry and N-terminal protein sequencing analysis revealed that the majority of the PK-resistant 37-kDa proteins in the urine of patients were outer membrane proteins (OMPs) of the Enterobacterial species. OMPs isolated from these bacteria were resistant to PK and the PK-resistant OMPs from the Enterobacterial species migrated around 37 kDa on SDS-PAGE. Furthermore, nonspecific binding of OMPs to antibodies could be mistaken for PrPSc. These findings caution that bacterial contamination can affect the immunological detection of prion protein. Therefore, the presence of Enterobacterial species should be excluded in the immunological tests for PrPSc in clinical samples, in particular, urine.

Original languageEnglish
Pages (from-to)23661-23667
Number of pages7
JournalJournal of Biological Chemistry
Volume279
Issue number22
DOIs
Publication statusPublished - May 28 2004

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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