JMSSJ On-line, Vol. 44 (1996) No. 6, pp. 641-652
Molecular Mass Measurement of Hydrophobic and Aggregative Virus Proteins to Confirm Sequence Variation and Post-translational Modification by Electrospray Ionization and Array Detection
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    Keiichiro ISHIKAWA,*a) Toshihiro OMURA,b) Yoshinori KOGA,a) Yoshio NIWA,a) and Masahiko TSUCHIYAc)

    *a) National Institute of Materials and Chemical Research (Higashi, Tsukuba 305, Japan) b) National Agriculture Research Center (Kannondai, Tsukuba 305, Japan) c) Faculty of Engineering, Yokohama National University (Tokiwadai, Hodogaya-ku, Yokohama 240, Japan)
Molecular mass measurements have been studied of outer capsid proteins (P8, -46 kDa) of rice dwarf virus (RDV) by electrospray ionization (ESI) and array detection on a high performance magnetic sector instrument. P8 proteins were highly hydrophobic and aggregative and, therefore, hardly soluble in ESI solvents. Use of an array detector was essential to compensate for the extremely low concentration of solubilized P8 proteins. Extensive tailing of the peak profiles of multiply charged proteins made it difficult to determine their center of gravity representing relative molecular masses (Mr). In stead of Mr, top positions of unresolved peak profiles were utilized which gave molecular masses of the most abundant isotope ions (Ma) at a precision of 0.002%. Precise Ma of P8 proteins suggested the presence of an yet unknown post-translational modification, which was identified as N-terminal acetylation by the sequence analysis of V8-protease digests by FAB-MS/MS. Further, a small difference in Ma (12.3±2.1 Da) between P8 proteins from the ordinary (RDV-O) and the severe (RDV-S) strains of RDV allowed the confirmation of the strain specific amino acid substitution predicted by nucleotide sequencing. The applicability of ESI-MS in combination with array detection was demonstrated for less soluble proteins of biological importance.
Key words: Viral protein, Molecular mass measurement, Electrospray ionization, Array detector
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