Related Experiment Video
Updated: Aug 15, 2026

Biotinylated Cell-penetrating Peptides to Study Intracellular Protein-protein Interactions
Published on: December 20, 2017
Bilin attachment sites in the alpha and beta subunits of B-phycoerythrin. Amino acid sequence studies
Abstract:
The amino acid sequence about the sites of attachment of all of the bilin prosthetic groups of the alpha and beta subunits of Porphyridium cruentum B-phycoerythrin has been determined. The sequences of five unique tryptic peptides, each carrying one phycoerythrobilin, are as follows: alpha-1 Ile-Asx-Lys-Cys*-Tyr-Arg alpha-2 Asx-Arg-Leu-Cys*-Val-Pro-Arg beta-1 Met-Ala-Ala-Cys*-Leu-Arg beta-2 Met-Ser-Phe-Ala-Ala-Gly-Asp-Cys*-Thr-Ser-Leu-Ala-Ser-Glu-Val-Ala-Gln-Tyr - Phe-Asp-Arg beta-3 Leu-Asp-Ala-Val-Asn-Ser-Ile-Val-Ser-Asn-Ala-Ser-Cys*-Met-Val-Ser-Asp-Ala - Val-Ser-Gly-Met-Ile-Cys*-Glu-Asn-Pro-Gly-Leu-Ile-Ser-Pro-Gly-Gly-Asn-Cys -Tyr- Thr-Asn-Arg where the designations alpha and beta refer to the subunit from which the peptide was derived. Cysteinyl residues involved in bilin attachment are indicated with an asterisk. The bilins in peptides alpha-1, alpha-2, beta-1, and beta-2 are attached to the peptide through a single thioether linkage to a cysteinyl residue. In contrast, the phycoerythrobilin on peptide beta-3 is attached through two thioether linkages to cysteinyl residues 10 residues apart. This appears to be the first report of a prosthetic group covalently bound to a polypeptide through two linkages separated by such a considerable distance in the linear sequence. The visible absorption spectrum of peptide beta-3 is red-shifted by about 10 nm relative to the spectra of the other four bilin peptides. Comparison of the sequences from B-phycoerythrin to sequences of several other biliproteins has revealed the presence of a number of invariant tyrosyl and arginyl residues near bilin attachment sites.
Related Concept Videos
Globular and Fibrous Proteins
Globular proteins are also known as spheroproteins and typically are approximately round in shape. They contain a mix of amino acid types and contain differing sequences in their primary structures. Globular proteins have many different functions, such as enzymes, cellular messengers, and molecular transporters. These roles often require the proteins to be...
Conserved Binding Sites
Binding sites are often located in large pockets, and if their location on a protein’s surface is unknown, it can be predicted using various approaches. The energetic method computationally analyses the...
Ligand Binding and Linkage
Directing Proteins to the Rough Endoplasmic Reticulum
Allosteric Proteins-ATCase
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
Multi-pass Transmembrane Proteins and β-barrels
α-Helix containing multi-pass transmembrane proteins
Multi-pass transmembrane proteins such as G-protein-linked receptors (GPCRs) and...

