Deep Dive

BPC-157Body Protection Compound 157

Every second, the stomach performs a task that should be impossible: it dissolves protein while being made of protein.

Something in gastric juice protects the stomach from what the stomach does. A laboratory in Zagreb spent decades isolating it. BPC-157 is fifteen amino acids taken from what they found.

Identity

1 What is it?

The stomach holds acid at pH 1 to 2 — a million times more acidic than blood — and fills it with pepsin, an enzyme whose entire function is cutting protein apart. The lining that contains all this is itself protein. It survives anyway.

That is where the Zagreb group started. Predrag Sikirić and colleagues at the University of Zagreb School of Medicine were working on gastric cytoprotection: what actively defends the mucosa, rather than what repairs it afterwards. Mucus and bicarbonate were the known answers. They went looking for a protein one.

They isolated a ~40 kDa gastric-juice protein and named it Body Protection Compound. Sequencing it from the N-terminus returned fifteen residues and no further — GEPPPGKPADDAGLV — and that N-terminal fragment, synthesised alone, is BPC-157.

Read the sequence and the compound begins to explain itself. GEPPPGKPADDAGLV. Four of those fifteen letters are proline — 26.7% of the chain, an unusually high proportion — and three sit consecutively, a triple-proline cluster at positions 3 to 5.

Proteins work by folding — a chain collapses into a specific shape, and that shape is the function, which is why heat and acid destroy most of them by unfolding that shape. Proline resists this: its side chain loops back and bonds its own backbone nitrogen, locking the hinge that other residues leave free. A chain this proline-rich, with three prolines in a row, cannot collapse into a single well-defined fold the way an ordinary protein does.

This is a plausible structural account of why BPC-157 might survive gastric juice — not a proven one. Protease resistance depends on the specific enzyme, the accessible cleavage sites, neighbouring residues, terminal chemistry, pH, and the assay used, and four prolines alone do not establish gastric stability. The sequence points to a likely contribution; the mechanism of its reported durability is not settled from composition alone.

That flexibility also frames the central difficulty. Molecular recognition often turns on shape, and a peptide that populates many conformations rather than one well-defined structure is harder to match to a single binding partner — though flexible peptides can still fold on binding or act through other routes. Whatever the reason, after more than thirty years no molecular target has been identified for this one.

2 How does it work?