ORDER BY custom type

Hi all.
 
I have this custom-type:
 
CREATE TYPE PERSONTYPE AS ( id BIGINT, firstname VARCHAR, lastname VARCHAR,
initialsVARCHAR );
 
I'm returning a column with this type using the following query, which lists
activities and its responsible-person (using the PERSONTYPE):
SELECT act.entity_id AS project_id, act.name AS project , (SELECT ROW
(p.entity_id, p.firstname, p.lastname, p.initials)::persontypeFROM
onp_crm_person pWHERE act.responsible = p.onp_user_id) AS responsible_person
fromonp_crm_activity act ORDER BY responsible_person ASC ;
 
But I need to ORDER BY different properties of PERSONTYPE, ie. initials, and
am wondering if there exists a mechanism to achieve the following:
SELECT act.entity_id AS project_id, act.name AS project , (SELECT ROW
(p.entity_id, p.firstname, p.lastname, p.initials)::persontypeFROM
onp_crm_person pWHERE act.responsible = p.onp_user_id) AS responsible_person
fromonp_crm_activity act ORDER BY responsible_person.initials ASC ;
How do I do that?
 
Thanks.
 
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