If you want a kind-of MAC which is such that it can be verified by using a "transformed key" which is itself not sufficient to compute other MAC values, then you do not want a MAC. What you want is a digital signature algorithm. One way to describe a digital signature algorithm is the following: it is like a MAC where the key for generating new MAC values, and the key for verifying a MAC value with regards to some data, are distinct. The two keys are mathematically linked with each other (the verification key works for MAC values which were generating with the corresponding generation key, and none other), but it is not feasible to recompute the generation key from the verification key. The verification key can thus be made public, while the generation key is kept private.
The most widely used signature algorithm is RSA (RSA is actually two algorithms, one for encryption and one for signatures; I am talking about the one for signatures; both algorithms share the same core mathematical operation, but are still quite different in their usage details).
HMAC is not a digital signature algorithm (despite what sloppy terminologists occasionally pretend).