Albumin fragments

Native bovine serum albumin has the surprising property of catalyzing the decomposition of the Meisenheimer complex 1,1-dihydro-2,4,6-trinitrocylohexadienate. Taylor and Silver (1976) prepared albumin fragments 1-306 and 307-581 and separated them without disulfide reduction. These were called native fragments. Neither of these fragments alone has catalytic activity to decompose the Meisenheimer complex, but when mixed together stoichiometrically, 35%... 

The N-terminal peptide fragment of des-angiotensinogen Val-Ile-His-Asn contains two strongly hydrophobic amino acid residues on the N-terminal site of His-3. The potentiometric data have shown that the NiH.2L complex with this albumin-like sequence is more than two orders of magnitude more stable than the respective complex with Gly-Gly-His.1744 The NMR-based molecular structure has shown that the side chains of Val-1 and lie-2 form a well-ordered hydrophobic fence (Figure 21) shielding one side of the coordination plane from the bulk of... 

Soltes, L., Sebille, B. (1997). Reversible binding interactions between the tryptophan enantiomers and albumins of different animal species as determined by novel high performance liquid chromatographic methods an attempt to localize the d- and L-tryptophan binding sites on the human serum albumin polypeptide chain by using protein fragments. Chirality 9, 373-379. 

Figure 6.4. Fragmentation spectrum of a tryptic peptide obtained from bovine serum albumin. Peptide sequence LGEYGFQNALIVR, monoisotopic [M + H]+ = 1479.796, monoisotopic [M+2H]2+ =740.402. Upper panel full scan MS spectrum. Lower panel MS/MS spectrum of a doubly-charged ion at 740.7 m/z with a ladder of y ions, the distances between which correspond to amino acid residues (upper row of letters). A shorter series of b ions is also seen (lower row of letters). See Fig. 6.5 for description of nomenclature. Note the often observed phenomenon where multiply-charged ions lose the charge during fragmentation process and, therefore, have higher m/z values than the original parent ion.

Complete sequencing of this peptide requires acquisition of additional tandem mass spectra, preferably MS3 fragmentation, of one of the low-mass y-ions. Because the peptide of interest is derived from a biological source, yet another possibility might be the use of sequence databases, similarly to the previous example. Actually, this approach works very well in this case, allowing identification of the peptide of interest as H-LGEYGFQNALIVR-OH, the 421-433 fragment of bovine serum albumin. 

A reversible, direct fluoroimmunosensor for human serum albumin (HS A) measurement has been described by Bright et al.(m> Antibody Fab fragments are first immobilized on small quartz plates by hinge-region thiols, and then dansylated. The immunosensor is formed by attaching the quartz plates with bound Fab to the distal end of a bifurcated fiber-optic probe, which transmits both the excitation and emission. Binding of ffSA to the immunosensor results in a three- to five-fold enhancement of dansyl fluorescence. The sensor can be reused up to 50 times, with a detection limit of about 1.8 x 10-8 M, and a somewhat limited dynamic range. 

Fig. 5. Schematic representation of the domain structure of albumin, the position of the disulfide loops, and the fragments of the molecule that have been isolated. Included in the figure are the cleavage methods used to obtain the fragments plus the regions to which the restricted antibody populations used in these experiments are directed. Reprinted, with permission, from Teale and Benjamin (1976). Copyright by the American Society of Biological Chemists, Inc.

That conclusion is supported and extended by the virtually simultaneous publication of Teale and Benjamin (1976). These investigators studied the oxidative regeneration of bovine serum albumin, assaying the extent of refolding immunochemically. Their results showed clearly that some parts of the molecule fold faster than others. Two fragments of albumin were tested for oxidative regeneration in the same way. Substantial return of native structure was seen in both fragments. 

Fig. 7. Kinetics of return of native antigenic structure in various limited regions of reduced albumin as determined with restricted populations of antialbumin. Reduced protein was reoxidized in the presence of optimal amounts of rat liver disulfide-exchange enzyme (0.5 mg/ml of RII/2.5 ml of reaction mixture). The reoxidation buffer and other conditions were as described in Section II. (A) 0, Anti-T 5 1M , anti- Tstt-mi anti-N-fragment antialbumin, anti-C-ffagment and anti anti-T,M, j.

In a subsequent paper, Teale and Benjamin (1977) carried out further experiments of the same kind with additional fragments of albumin. They concluded that the C-terminal one-third of each of the... 

Folding to native-like structure has been demonstrated with fragments of jS-galactosidase, lysozyme, serum albumin, penicillinase, and tryptophan synthetase. The capability of protein fragments for independent formation of structure therefore has substantial experimental basis. This generalization also makes plausible the idea that, in general, protein folding occurs by parts, that is, in a modular fashion. 

Example The reduced sample consumption of nanoESI allows for the sequencing of the peptides (Chap. 9.4.7) obtained by tryptic digestion of only 800 fmol of the protein bovine semm albumin (BSA, Fig. 11.6). [66] The experiment depicted below requires each of the BSA-derived peptide ions in the full scan spectrum to be subjected to fragment ion analysis by means of CID-MS/MS on a triple quadrupole instmment (Chaps. 2.12 and 4.4.5). 

Fig. 11.6. Peptide sequencing by nanoESI-CID-MS/MS from a tryptic digest of bovine serum albumin (BSA) 800 fmol of BSA were used, (a) Eull scan spectrum, (b) fragmentation of the selected doubly charged peptide ion at m/z 740.5. Adapted from Ref. [66] by permission. Nature Publishing Group, 1996.

FIGURE 4 Effect of sample preparation on the fragmentation of an rMAb observed in (A) SDS-PAGE and (B) CE-SDS with LIF detection. SDS-PAGE lanes (Lane I) molecular weight standards bovine serum albumin at (Lane 2) 8 ng and (Lane 3) 2 ng (Lane 4) rMAb control after alkylation with (Lane 5) iodoacetic acid and (Lane 6) iodoacetamide. (See color plate 4.)... 

Similar to the approaches followed with cyanine dyes (Chapter 3.1.3), attempts to enhance the selectivity of photosensitizers by conjugating to target-specific vehicles have been described [98]. The approaches included conjugates with antibodies [99, 100], antibody fragments [58, 101], peptides [102], the serum proteins albumin and transferrin [103,104] and estradiol [105]. 

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