The present disclosure relates to a collection of novel muteins derived from human α1m (or a1m) polypeptide or a functional homologue thereof. The disclosure further refers to a α1m mutein capable of specifically binding to one or more targets other than a target to which wild-type α1m binds. The disclosure also relates to a method for producing such collection of muteins and a method for isolating a mutein capable of binding one or more such non-natural targets of wild-type α1m polypeptide. These aspects are made possible due to, e.g, the structural elucidation of α1m disclosed herein by the present inventors, an appreciation of ligand-binding sights thereof and, hence, an understanding of which amino acid positions are most suitable for mutagenesis for re-engineering specificity and affinity for any given target while maintaining the secondary and/or tertiary structure of a1m.
