Table I

Assignment M2AP C-terminal cleavage sites based on MALDI intact masses

Mature M2AP (mM2AP) and its truncated products (M2AP1–4) were resolved on 2DE gels (Fig. 1, B and C), excised, and solvent-extracted. Their intact masses were analyzed by MALDI-TOF MS (Fig. 1D). The sizes of the truncated fragments of M2AP1–4 were calculated by subtracting their masses from that of mM2AP.

SpeciesMeasured intact massaMass difference from mM2APbMass deviation (cleavage site)c
mM2AP30,438.35 ± 14.5600
M2AP-127,319.87 ± 13.063,118.48 ± 26.989.34 (Q256/E257)
M2AP-223,621.91 ± 21.796,816.44 ± 36.2631.48 (L222/S223)
M2AP-322,057.39 ± 11.768,380.96 ± 24.7127.34 (A207/E208)
M2AP-421,762.38 ± 31.628,675.96 ± 43.2318.04 (S203/A204)
  • a Intact mass (± S.D., triplicate measurements) measured by MALDI-TOF MS as described in “Experimental Procedures.”

  • b Mass (± S.D., triplicate measurements) difference determined by subtracting the measured intact masses of M2AP1–4 from the measured mass of mM2AP.

  • c Mass deviation from the calculated value based on the cleavage site shown in parentheses.