An immunolglobulin light chain-like protein composed of an immunoglobulin variable region-like peptide (such as light chain like lambda5 peptide) and an IMMUNOGLOBULIN CONSTANT REGION-like peptide (such as Vpreb1 peptide). Surrogate light chains associate with MU immunoglobulin heavy chains in place of a conventional immunoglobulin light chains to form pre-b cell receptors.