Hi Javier,
STEP is a complicated format, and I doubt you will find a general-purpose importer function that is versatile enough to import all possible keywords that can appear in a STEP file. Further, because Matlab is not a CAD program, several common CAD features, such as curved faces, extrudes, etc. are not natively defined in Matlab, and in fact do not necessarily have such meaning.
Instead, I would look at the .STEP file itself (using a text editor such as Notepad) and see if you can figure out which elements of the file are relevant to you. Once you have a better idea of what information you want to extract from the file, we might be able to provide more information.
