Provided herein relate to modified or mutant forms of cytolysin A (ClyA) and compositions comprising the same. In particular, the modified or mutant forms of ClyA permits efficient capture and/or translocation of a target negative-charged molecule or polymer through the modified or mutant ClyA nanopores at low or physiological ionic strengths. Thus, methods for using the modified or mutant forms of ClyA and compositions, for example, for characterizing a target negatively-charged analyte, e.g., a target polynucleotide, are also provided.