The subcellular localization and targeting pathway of hyaluronidase 1

Hyaluronidases are endoglycosidases that catabolize hyaluronan, an abundant component of the extracellular matrix surrounding vertebrate cells. We characterized one of the hyaluronidases, HYAL1, an enzyme deficient in the lysosomal storage disorder Mucopolysaccharidosis IX. HYAL1 stably expressed in BHK cells resulted in several intracellular forms, but only one secreted form. Secretion was not increased by weak bases, and no phosphate was incorporated in metabolic labeling, suggesting this enzyme is not targeted to the lysosome by the mannose 6-phosphate dependent pathway. Further analysis revealed the various forms of HYAL1 differ only in glycosylation, and are all active at pH 3.8. The forms migrated in a Percol density gradient similarly to an endosomal marker, and with partial overlap with the lysosomal marker LPG120 (Lamp1).