Figure 4
From: Mechanisms underlying ICU muscle wasting and effects of passive mechanical loading
Post-translational modifications of the myosin motor domain. (A) Ribbon diagram of the myosin motor domain (red) and part of the tail region (blue). Three ICU-condition-specific post-translational modifications (PTMs) were observed in the motor domain of the protein (yellow) and one lost modification was in the tail region (green). Since only part of the myosin protein is modeled, PTMs located further down on the tail region are not shown. (B) Upper panel, spectrum of deamidated peptide ENQSILITGESGAGK; bottom panel, spectrum of intact peptide ENQSILITGESGAGK. The deamidation is safely determined by high-resolution mass spectrometry (MS) in MS mode (the mass difference between the molecular ion masses is 0.984 Da, corresponding to N+H-O) and in MS/MS mode as well. In the MS/MS spectrum one can see the mass shift of +1 Da for all b-ion series, including those that correspond to neutral losses from b-ions, except b2. Since b2 ion has the same mass for both peptides and contains asparagine, the deamidation is assigned to glutamine Gln3 and not Asn2.